From dc36f0de53bc1ec9ed06333f80403ca55894dd5d Mon Sep 17 00:00:00 2001 From: 30secondsofcode <30secondsofcode@gmail.com> Date: Wed, 23 May 2018 21:13:34 +0000 Subject: [PATCH 1/7] Travis build: 2085 [cron] --- docs/index.html | 51 +++++++++++++++++++++++-------------------------- test/testlog | 6 +++--- 2 files changed, 27 insertions(+), 30 deletions(-) diff --git a/docs/index.html b/docs/index.html index 0d7c5869a..b0df6bd91 100644 --- a/docs/index.html +++ b/docs/index.html @@ -1,33 +1,30 @@ -30 seconds of code

logo 30 seconds of code

Curated collection of useful JavaScript snippets
that you can understand in 30 seconds or less.

304
snippets

118
contributors

3232
commits

20066
stars

Our philosophy

The core goal of 30 seconds of code is to provide a quality resource for beginner and advanced JavaScript developers alike. We want to help improve the JavaScript ecosystem, by lowering the barrier of entry for newcomers and help seasoned veterans pick up new tricks and remember old ones. In order to achieve this, we have collected hundreds of snippets that can be of use in a wide range of situations. We welcome new contributors and we like fresh ideas, as long as the code is short and easy to grasp in about 30 seconds. The only catch, if you may, is that many of our snippets are not perfectly suited for large, enterprise applications and they might not be deemed production-ready.


In order for 30 seconds of code to be as accessible and useful as possible, all of the snippets in the collection are licensed under the CC0-1.0 License, meaning they are absolutely free to use in any project you like. If you like what we do, you can always credit us, but that is not mandatory.


Today's picks

Our sophisticated robot helpers pick new snippets from our collection daily, so that you can discover new snippets to enhance your projects:

on

Adds an event listener to an element with the ability to use event delegation.

Use EventTarget.addEventListener() to add an event listener to an element. If there is a target property supplied to the options object, ensure the event target matches the target specified and then invoke the callback by supplying the correct this context. Returns a reference to the custom delegator function, in order to be possible to use with off. Omit opts to default to non-delegation behavior and event bubbling.

const on = (el, evt, fn, opts = {}) => {
-  const delegatorFn = e => e.target.matches(opts.target) && fn.call(e.target, e);
-  el.addEventListener(evt, opts.target ? delegatorFn : fn, opts.options || false);
-  if (opts.target) return delegatorFn;
+30 seconds of code
logo 30 seconds of code
Curated collection of useful JavaScript snippets
that you can understand in 30 seconds or less.
304
snippets
118
contributors
3233
commits
20080
stars
Our philosophy
The core goal of 30 seconds of code is to provide a quality resource for beginner and advanced JavaScript developers alike. We want to help improve the JavaScript ecosystem, by lowering the barrier of entry for newcomers and help seasoned veterans pick up new tricks and remember old ones. In order to achieve this, we have collected hundreds of snippets that can be of use in a wide range of situations. We welcome new contributors and we like fresh ideas, as long as the code is short and easy to grasp in about 30 seconds. The only catch, if you may, is that many of our snippets are not perfectly suited for large, enterprise applications and they might not be deemed production-ready.

In order for 30 seconds of code to be as accessible and useful as possible, all of the snippets in the collection are licensed under the CC0-1.0 License, meaning they are absolutely free to use in any project you like. If you like what we do, you can always credit us, but that is not mandatory.

Today's picks
Our sophisticated robot helpers pick new snippets from our collection daily, so that you can discover new snippets to enhance your projects:
 
converge
Accepts a converging function and a list of branching functions and returns a function that applies each branching function to the arguments and the results of the branching functions are passed as arguments to the converging function.
Use Array.map() and Function.apply() to apply each function to the given arguments. Use the spread operator (...) to call coverger with the results of all other functions.
const converge = (converger, fns) => (...args) => converger(...fns.map(fn => fn.apply(null, args)));
+
const average = converge((a, b) => a / b, [
+  arr => arr.reduce((a, v) => a + v, 0),
+  arr => arr.length
+]);
+average([1, 2, 3, 4, 5, 6, 7]); // 4
+
mapValues
Creates an object with the same keys as the provided object and values generated by running the provided function for each value.
Use Object.keys(obj) to iterate over the object's keys. Use Array.reduce() to create a new object with the same keys and mapped values using fn.
const mapValues = (obj, fn) =>
+  Object.keys(obj).reduce((acc, k) => {
+    acc[k] = fn(obj[k], k, obj);
+    return acc;
+  }, {});
+
const users = {
+  fred: { user: 'fred', age: 40 },
+  pebbles: { user: 'pebbles', age: 1 }
 };
-
const fn = () => console.log('!');
-on(document.body, 'click', fn); // logs '!' upon clicking the body
-on(document.body, 'click', fn, { target: 'p' }); // logs '!' upon clicking a `p` element child of the body
-on(document.body, 'click', fn, { options: true }); // use capturing instead of bubbling
-
randomHexColorCode
Generates a random hexadecimal color code.
Use Math.random to generate a random 24-bit(6x4bits) hexadecimal number. Use bit shifting and then convert it to an hexadecimal String using toString(16).
const randomHexColorCode = () => {
-  let n = (Math.random() * 0xfffff * 1000000).toString(16);
-  return '#' + n.slice(0, 6);
-};
-
randomHexColorCode(); // "#e34155"
-
unescapeHTML
Unescapes escaped HTML characters.
Use String.replace() with a regex that matches the characters that need to be unescaped, using a callback function to replace each escaped character instance with its associated unescaped character using a dictionary (object).
const unescapeHTML = str =>
-  str.replace(
-    /&amp;|&lt;|&gt;|&#39;|&quot;/g,
-    tag =>
-      ({
-        '&amp;': '&',
-        '&lt;': '<',
-        '&gt;': '>',
-        '&#39;': "'",
-        '&quot;': '"'
-      }[tag] || tag)
-  );
-
unescapeHTML('&lt;a href=&quot;#&quot;&gt;Me &amp; you&lt;/a&gt;'); // '<a href="#">Me & you</a>'
+mapValues(users, u => u.age); // { fred: 40, pebbles: 1 }
+
sumPower
Returns the sum of the powers of all the numbers from start to end (both inclusive).
Use Array.fill() to create an array of all the numbers in the target range, Array.map() and the exponent operator (**) to raise them to power and Array.reduce() to add them together. Omit the second argument, power, to use a default power of 2. Omit the third argument, start, to use a default starting value of 1.
const sumPower = (end, power = 2, start = 1) =>
+  Array(end + 1 - start)
+    .fill(0)
+    .map((x, i) => (i + start) ** power)
+    .reduce((a, b) => a + b, 0);
+
sumPower(10); // 385
+sumPower(10, 3); //3025
+sumPower(10, 3, 5); //2925
 

Getting started

Related projects
The idea behind 30 seconds of code has inspired some people to create similar collections in other programming languages and environments. Here are the ones we like the most:

Top contributors
chalarangelo Angelos Chalaris
fejes713 Stefan Feješ
flxwu Felix Wu
atomiks atomiks
kingdavidmartins King David Martins
kriadmin Rohit Tanwar
iamsoorena Soorena Soleimani
skatcat31 Robert Mennell
How to contribute
Do you have a cool idea for a new snippet? Maybe some code you use often and is not part of our collection? Contributing to 30 seconds of code is as simple as 1,2,3,4!
1
Create
Start by creating a snippet, according to the snippet template. Make sure to follow these simple guidelines:
  • Your snippet title must be unique and the same as the name of the implemented function.
  • Use the snippet description to explain what your snippet does and how it works.
  • Try to keep the snippet's code short and to the point. Use modern techniques and features.
  • Remember to provide an example of how your snippet works.
  • Your snippet should solve a real-world problem, no matter how simple.
  • Never modify README.md or any of the HTML files.
2
Tag
Run npm run tagger from your terminal, then open the tag_database file and tag your snippet appropriately. Multitagging is also supported, just make sure the first tag you specify is on of the major tags and the one that is most relevant to the implemneted function.
3
Test
You can optionally test your snippet to make our job easier. Simply run npm run tester to generate the test files for your snippet. Find the related folder for you snippet under the test directory and write some tests. Remember to run npm run tester again to make sure your tests are passing.
4
Pull request
If you have done everything mentioned above, you should now have an awesome snippet to add to our collection. Simply start a pull request and follow the guidelines provided. Remember to only submit one snippet per pull request, so that we can quickly evaluate and merge your code into the collection.
If you need additional pointers about writing a snippet, be sure to read the complete contribution guidelines.

30 seconds of code
logo 30 seconds of code
Curated collection of useful JavaScript snippets
that you can understand in 30 seconds or less.
304
snippets
118
contributors
3233
commits
20080
stars
Our philosophy
The core goal of 30 seconds of code is to provide a quality resource for beginner and advanced JavaScript developers alike. We want to help improve the JavaScript ecosystem, by lowering the barrier of entry for newcomers and help seasoned veterans pick up new tricks and remember old ones. In order to achieve this, we have collected hundreds of snippets that can be of use in a wide range of situations. We welcome new contributors and we like fresh ideas, as long as the code is short and easy to grasp in about 30 seconds. The only catch, if you may, is that many of our snippets are not perfectly suited for large, enterprise applications and they might not be deemed production-ready.

In order for 30 seconds of code to be as accessible and useful as possible, all of the snippets in the collection are licensed under the CC0-1.0 License, meaning they are absolutely free to use in any project you like. If you like what we do, you can always credit us, but that is not mandatory.

Today's picks
Our sophisticated robot helpers pick new snippets from our collection daily, so that you can discover new snippets to enhance your projects:
 
converge
Accepts a converging function and a list of branching functions and returns a function that applies each branching function to the arguments and the results of the branching functions are passed as arguments to the converging function.
Use Array.map() and Function.apply() to apply each function to the given arguments. Use the spread operator (...) to call coverger with the results of all other functions.
const converge = (converger, fns) => (...args) => converger(...fns.map(fn => fn.apply(null, args)));
-
const average = converge((a, b) => a / b, [
-  arr => arr.reduce((a, v) => a + v, 0),
-  arr => arr.length
-]);
-average([1, 2, 3, 4, 5, 6, 7]); // 4
-
mapValues
Creates an object with the same keys as the provided object and values generated by running the provided function for each value.
Use Object.keys(obj) to iterate over the object's keys. Use Array.reduce() to create a new object with the same keys and mapped values using fn.
const mapValues = (obj, fn) =>
-  Object.keys(obj).reduce((acc, k) => {
-    acc[k] = fn(obj[k], k, obj);
-    return acc;
-  }, {});
-
const users = {
-  fred: { user: 'fred', age: 40 },
-  pebbles: { user: 'pebbles', age: 1 }
+30 seconds of code
logo 30 seconds of code
Curated collection of useful JavaScript snippets
that you can understand in 30 seconds or less.
304
snippets
118
contributors
3234
commits
20088
stars
Our philosophy
The core goal of 30 seconds of code is to provide a quality resource for beginner and advanced JavaScript developers alike. We want to help improve the JavaScript ecosystem, by lowering the barrier of entry for newcomers and help seasoned veterans pick up new tricks and remember old ones. In order to achieve this, we have collected hundreds of snippets that can be of use in a wide range of situations. We welcome new contributors and we like fresh ideas, as long as the code is short and easy to grasp in about 30 seconds. The only catch, if you may, is that many of our snippets are not perfectly suited for large, enterprise applications and they might not be deemed production-ready.

In order for 30 seconds of code to be as accessible and useful as possible, all of the snippets in the collection are licensed under the CC0-1.0 License, meaning they are absolutely free to use in any project you like. If you like what we do, you can always credit us, but that is not mandatory.

Today's picks
Our sophisticated robot helpers pick new snippets from our collection daily, so that you can discover new snippets to enhance your projects:
 
maxN
Returns the n maximum elements from the provided array. If n is greater than or equal to the provided array's length, then return the original array(sorted in descending order).
Use Array.sort() combined with the spread operator (...) to create a shallow clone of the array and sort it in descending order. Use Array.slice() to get the specified number of elements. Omit the second argument, n, to get a one-element array.
const maxN = (arr, n = 1) => [...arr].sort((a, b) => b - a).slice(0, n);
+
maxN([1, 2, 3]); // [3]
+maxN([1, 2, 3], 2); // [3,2]
+
rearg
Creates a function that invokes the provided function with its arguments arranged according to the specified indexes.
Use Array.reduce() and Array.indexOf() to reorder arguments based on indexes in combination with the spread operator (...) to pass the transformed arguments to fn.
const rearg = (fn, indexes) => (...args) =>
+  fn(
+    ...args.reduce(
+      (acc, val, i) => ((acc[indexes.indexOf(i)] = val), acc),
+      Array.from({ length: indexes.length })
+    )
+  );
+
var rearged = rearg(
+  function(a, b, c) {
+    return [a, b, c];
+  },
+  [2, 0, 1]
+);
+rearged('b', 'c', 'a'); // ['a', 'b', 'c']
+
recordAnimationFrames
Invokes the provided callback on each animation frame.
Use recursion. Provided that running is true, continue invoking window.requestAnimationFrame() which invokes the provided callback. Return an object with two methods start and stop to allow manual control of the recording. Omit the second argument, autoStart, to implicitly call start when the function is invoked.
const recordAnimationFrames = (callback, autoStart = true) => {
+  let running = true,
+    raf;
+  const stop = () => {
+    running = false;
+    cancelAnimationFrame(raf);
+  };
+  const start = () => {
+    running = true;
+    run();
+  };
+  const run = () => {
+    raf = requestAnimationFrame(() => {
+      callback();
+      if (running) run();
+    });
+  };
+  if (autoStart) start();
+  return { start, stop };
 };
-mapValues(users, u => u.age); // { fred: 40, pebbles: 1 }
-
sumPower
Returns the sum of the powers of all the numbers from start to end (both inclusive).
Use Array.fill() to create an array of all the numbers in the target range, Array.map() and the exponent operator (**) to raise them to power and Array.reduce() to add them together. Omit the second argument, power, to use a default power of 2. Omit the third argument, start, to use a default starting value of 1.
const sumPower = (end, power = 2, start = 1) =>
-  Array(end + 1 - start)
-    .fill(0)
-    .map((x, i) => (i + start) ** power)
-    .reduce((a, b) => a + b, 0);
-
sumPower(10); // 385
-sumPower(10, 3); //3025
-sumPower(10, 3, 5); //2925
+
const cb = () => console.log('Animation frame fired');
+const recorder = recordAnimationFrames(cb); // logs 'Animation frame fired' on each animation frame
+recorder.stop(); // stops logging
+recorder.start(); // starts again
+const recorder2 = recordAnimationFrames(cb, false); // `start` needs to be explicitly called to begin recording frames
 

Getting started

Related projects
The idea behind 30 seconds of code has inspired some people to create similar collections in other programming languages and environments. Here are the ones we like the most:

Top contributors
chalarangelo Angelos Chalaris
fejes713 Stefan Feješ
flxwu Felix Wu
atomiks atomiks
kingdavidmartins King David Martins
kriadmin Rohit Tanwar
iamsoorena Soorena Soleimani
skatcat31 Robert Mennell
How to contribute
Do you have a cool idea for a new snippet? Maybe some code you use often and is not part of our collection? Contributing to 30 seconds of code is as simple as 1,2,3,4!
1
Create
Start by creating a snippet, according to the snippet template. Make sure to follow these simple guidelines:
  • Your snippet title must be unique and the same as the name of the implemented function.
  • Use the snippet description to explain what your snippet does and how it works.
  • Try to keep the snippet's code short and to the point. Use modern techniques and features.
  • Remember to provide an example of how your snippet works.
  • Your snippet should solve a real-world problem, no matter how simple.
  • Never modify README.md or any of the HTML files.
2
Tag
Run npm run tagger from your terminal, then open the tag_database file and tag your snippet appropriately. Multitagging is also supported, just make sure the first tag you specify is on of the major tags and the one that is most relevant to the implemneted function.
3
Test
You can optionally test your snippet to make our job easier. Simply run npm run tester to generate the test files for your snippet. Find the related folder for you snippet under the test directory and write some tests. Remember to run npm run tester again to make sure your tests are passing.
4
Pull request
If you have done everything mentioned above, you should now have an awesome snippet to add to our collection. Simply start a pull request and follow the guidelines provided. Remember to only submit one snippet per pull request, so that we can quickly evaluate and merge your code into the collection.
If you need additional pointers about writing a snippet, be sure to read the complete contribution guidelines.

30 seconds of code
logo 30 seconds of code
Curated collection of useful JavaScript snippets
that you can understand in 30 seconds or less.
304
snippets
118
contributors
3234
commits
20088
stars
Our philosophy
The core goal of 30 seconds of code is to provide a quality resource for beginner and advanced JavaScript developers alike. We want to help improve the JavaScript ecosystem, by lowering the barrier of entry for newcomers and help seasoned veterans pick up new tricks and remember old ones. In order to achieve this, we have collected hundreds of snippets that can be of use in a wide range of situations. We welcome new contributors and we like fresh ideas, as long as the code is short and easy to grasp in about 30 seconds. The only catch, if you may, is that many of our snippets are not perfectly suited for large, enterprise applications and they might not be deemed production-ready.

In order for 30 seconds of code to be as accessible and useful as possible, all of the snippets in the collection are licensed under the CC0-1.0 License, meaning they are absolutely free to use in any project you like. If you like what we do, you can always credit us, but that is not mandatory.

Today's picks
Our sophisticated robot helpers pick new snippets from our collection daily, so that you can discover new snippets to enhance your projects:
 
maxN
Returns the n maximum elements from the provided array. If n is greater than or equal to the provided array's length, then return the original array(sorted in descending order).
Use Array.sort() combined with the spread operator (...) to create a shallow clone of the array and sort it in descending order. Use Array.slice() to get the specified number of elements. Omit the second argument, n, to get a one-element array.
const maxN = (arr, n = 1) => [...arr].sort((a, b) => b - a).slice(0, n);
-
maxN([1, 2, 3]); // [3]
-maxN([1, 2, 3], 2); // [3,2]
-
rearg
Creates a function that invokes the provided function with its arguments arranged according to the specified indexes.
Use Array.reduce() and Array.indexOf() to reorder arguments based on indexes in combination with the spread operator (...) to pass the transformed arguments to fn.
const rearg = (fn, indexes) => (...args) =>
-  fn(
-    ...args.reduce(
-      (acc, val, i) => ((acc[indexes.indexOf(i)] = val), acc),
-      Array.from({ length: indexes.length })
-    )
-  );
-
var rearged = rearg(
-  function(a, b, c) {
-    return [a, b, c];
+30 seconds of code
logo 30 seconds of code
Curated collection of useful JavaScript snippets
that you can understand in 30 seconds or less.
304
snippets
118
contributors
3235
commits
20098
stars
Our philosophy
The core goal of 30 seconds of code is to provide a quality resource for beginner and advanced JavaScript developers alike. We want to help improve the JavaScript ecosystem, by lowering the barrier of entry for newcomers and help seasoned veterans pick up new tricks and remember old ones. In order to achieve this, we have collected hundreds of snippets that can be of use in a wide range of situations. We welcome new contributors and we like fresh ideas, as long as the code is short and easy to grasp in about 30 seconds. The only catch, if you may, is that many of our snippets are not perfectly suited for large, enterprise applications and they might not be deemed production-ready.

In order for 30 seconds of code to be as accessible and useful as possible, all of the snippets in the collection are licensed under the CC0-1.0 License, meaning they are absolutely free to use in any project you like. If you like what we do, you can always credit us, but that is not mandatory.

Today's picks
Our sophisticated robot helpers pick new snippets from our collection daily, so that you can discover new snippets to enhance your projects:
 
isBrowserTabFocused
Returns true if the browser tab of the page is focused, false otherwise.
Use the Document.hidden property, introduced by the Page Visibility API to check if the browser tab of the page is visible or hidden.
const isBrowserTabFocused = () => !document.hidden;
+
isBrowserTabFocused(); // true
+
transform
Applies a function against an accumulator and each key in the object (from left to right).
Use Object.keys(obj) to iterate over each key in the object, Array.reduce() to call the apply the specified function against the given accumulator.
const transform = (obj, fn, acc) => Object.keys(obj).reduce((a, k) => fn(a, obj[k], k, obj), acc);
+
transform(
+  { a: 1, b: 2, c: 1 },
+  (r, v, k) => {
+    (r[v] || (r[v] = [])).push(k);
+    return r;
   },
-  [2, 0, 1]
-);
-rearged('b', 'c', 'a'); // ['a', 'b', 'c']
-
recordAnimationFrames
Invokes the provided callback on each animation frame.
Use recursion. Provided that running is true, continue invoking window.requestAnimationFrame() which invokes the provided callback. Return an object with two methods start and stop to allow manual control of the recording. Omit the second argument, autoStart, to implicitly call start when the function is invoked.
const recordAnimationFrames = (callback, autoStart = true) => {
-  let running = true,
-    raf;
-  const stop = () => {
-    running = false;
-    cancelAnimationFrame(raf);
-  };
-  const start = () => {
-    running = true;
-    run();
-  };
-  const run = () => {
-    raf = requestAnimationFrame(() => {
-      callback();
-      if (running) run();
-    });
-  };
-  if (autoStart) start();
-  return { start, stop };
-};
-
const cb = () => console.log('Animation frame fired');
-const recorder = recordAnimationFrames(cb); // logs 'Animation frame fired' on each animation frame
-recorder.stop(); // stops logging
-recorder.start(); // starts again
-const recorder2 = recordAnimationFrames(cb, false); // `start` needs to be explicitly called to begin recording frames
+  {}
+); // { '1': ['a', 'c'], '2': ['b'] }
+
UUIDGeneratorBrowser
Generates a UUID in a browser.
Use crypto API to generate a UUID, compliant with RFC4122 version 4.
const UUIDGeneratorBrowser = () =>
+  ([1e7] + -1e3 + -4e3 + -8e3 + -1e11).replace(/[018]/g, c =>
+    (c ^ (crypto.getRandomValues(new Uint8Array(1))[0] & (15 >> (c / 4)))).toString(16)
+  );
+
UUIDGeneratorBrowser(); // '7982fcfe-5721-4632-bede-6000885be57d'
 

Getting started

Related projects
The idea behind 30 seconds of code has inspired some people to create similar collections in other programming languages and environments. Here are the ones we like the most:

Top contributors
chalarangelo Angelos Chalaris
fejes713 Stefan Feješ
flxwu Felix Wu
atomiks atomiks
kingdavidmartins King David Martins
kriadmin Rohit Tanwar
iamsoorena Soorena Soleimani
skatcat31 Robert Mennell
How to contribute
Do you have a cool idea for a new snippet? Maybe some code you use often and is not part of our collection? Contributing to 30 seconds of code is as simple as 1,2,3,4!
1
Create
Start by creating a snippet, according to the snippet template. Make sure to follow these simple guidelines:
  • Your snippet title must be unique and the same as the name of the implemented function.
  • Use the snippet description to explain what your snippet does and how it works.
  • Try to keep the snippet's code short and to the point. Use modern techniques and features.
  • Remember to provide an example of how your snippet works.
  • Your snippet should solve a real-world problem, no matter how simple.
  • Never modify README.md or any of the HTML files.
2
Tag
Run npm run tagger from your terminal, then open the tag_database file and tag your snippet appropriately. Multitagging is also supported, just make sure the first tag you specify is on of the major tags and the one that is most relevant to the implemneted function.
3
Test
You can optionally test your snippet to make our job easier. Simply run npm run tester to generate the test files for your snippet. Find the related folder for you snippet under the test directory and write some tests. Remember to run npm run tester again to make sure your tests are passing.
4
Pull request
If you have done everything mentioned above, you should now have an awesome snippet to add to our collection. Simply start a pull request and follow the guidelines provided. Remember to only submit one snippet per pull request, so that we can quickly evaluate and merge your code into the collection.
If you need additional pointers about writing a snippet, be sure to read the complete contribution guidelines.

30 seconds of code
logo 30 seconds of code
Curated collection of useful JavaScript snippets
that you can understand in 30 seconds or less.
304
snippets
118
contributors
3235
commits
20098
stars
Our philosophy
The core goal of 30 seconds of code is to provide a quality resource for beginner and advanced JavaScript developers alike. We want to help improve the JavaScript ecosystem, by lowering the barrier of entry for newcomers and help seasoned veterans pick up new tricks and remember old ones. In order to achieve this, we have collected hundreds of snippets that can be of use in a wide range of situations. We welcome new contributors and we like fresh ideas, as long as the code is short and easy to grasp in about 30 seconds. The only catch, if you may, is that many of our snippets are not perfectly suited for large, enterprise applications and they might not be deemed production-ready.

In order for 30 seconds of code to be as accessible and useful as possible, all of the snippets in the collection are licensed under the CC0-1.0 License, meaning they are absolutely free to use in any project you like. If you like what we do, you can always credit us, but that is not mandatory.

Today's picks
Our sophisticated robot helpers pick new snippets from our collection daily, so that you can discover new snippets to enhance your projects:
 
isBrowserTabFocused
Returns true if the browser tab of the page is focused, false otherwise.
Use the Document.hidden property, introduced by the Page Visibility API to check if the browser tab of the page is visible or hidden.
const isBrowserTabFocused = () => !document.hidden;
-
isBrowserTabFocused(); // true
-
transform
Applies a function against an accumulator and each key in the object (from left to right).
Use Object.keys(obj) to iterate over each key in the object, Array.reduce() to call the apply the specified function against the given accumulator.
const transform = (obj, fn, acc) => Object.keys(obj).reduce((a, k) => fn(a, obj[k], k, obj), acc);
-
transform(
-  { a: 1, b: 2, c: 1 },
-  (r, v, k) => {
-    (r[v] || (r[v] = [])).push(k);
-    return r;
-  },
-  {}
-); // { '1': ['a', 'c'], '2': ['b'] }
-
UUIDGeneratorBrowser
Generates a UUID in a browser.
Use crypto API to generate a UUID, compliant with RFC4122 version 4.
const UUIDGeneratorBrowser = () =>
-  ([1e7] + -1e3 + -4e3 + -8e3 + -1e11).replace(/[018]/g, c =>
-    (c ^ (crypto.getRandomValues(new Uint8Array(1))[0] & (15 >> (c / 4)))).toString(16)
+30 seconds of code
logo 30 seconds of code
Curated collection of useful JavaScript snippets
that you can understand in 30 seconds or less.
304
snippets
118
contributors
3236
commits
20104
stars
Our philosophy
The core goal of 30 seconds of code is to provide a quality resource for beginner and advanced JavaScript developers alike. We want to help improve the JavaScript ecosystem, by lowering the barrier of entry for newcomers and help seasoned veterans pick up new tricks and remember old ones. In order to achieve this, we have collected hundreds of snippets that can be of use in a wide range of situations. We welcome new contributors and we like fresh ideas, as long as the code is short and easy to grasp in about 30 seconds. The only catch, if you may, is that many of our snippets are not perfectly suited for large, enterprise applications and they might not be deemed production-ready.

In order for 30 seconds of code to be as accessible and useful as possible, all of the snippets in the collection are licensed under the CC0-1.0 License, meaning they are absolutely free to use in any project you like. If you like what we do, you can always credit us, but that is not mandatory.

Today's picks
Our sophisticated robot helpers pick new snippets from our collection daily, so that you can discover new snippets to enhance your projects:
 
isNumber
Checks if the given argument is a number.
Use typeof to check if a value is classified as a number primitive.
const isNumber = val => typeof val === 'number';
+
isNumber('1'); // false
+isNumber(1); // true
+
matchesWith
Compares two objects to determine if the first one contains equivalent property values to the second one, based on a provided function.
Use Object.keys(source) to get all the keys of the second object, then Array.every(), Object.hasOwnProperty() and the provided function to determine if all keys exist in the first object and have equivalent values. If no function is provided, the values will be compared using the equality operator.
const matchesWith = (obj, source, fn) =>
+  Object.keys(source).every(
+    key =>
+      obj.hasOwnProperty(key) && fn
+        ? fn(obj[key], source[key], key, obj, source)
+        : obj[key] == source[key]
   );
-
UUIDGeneratorBrowser(); // '7982fcfe-5721-4632-bede-6000885be57d'
+
const isGreeting = val => /^h(?:i|ello)$/.test(val);
+matchesWith(
+  { greeting: 'hello' },
+  { greeting: 'hi' },
+  (oV, sV) => isGreeting(oV) && isGreeting(sV)
+); // true
+
setStyle
Sets the value of a CSS rule for the specified element.
Use element.style to set the value of the CSS rule for the specified element to val.
const setStyle = (el, ruleName, val) => (el.style[ruleName] = val);
+
setStyle(document.querySelector('p'), 'font-size', '20px'); // The first <p> element on the page will have a font-size of 20px
 

Getting started

Related projects
The idea behind 30 seconds of code has inspired some people to create similar collections in other programming languages and environments. Here are the ones we like the most:

Top contributors
chalarangelo Angelos Chalaris
fejes713 Stefan Feješ
flxwu Felix Wu
atomiks atomiks
kingdavidmartins King David Martins
kriadmin Rohit Tanwar
iamsoorena Soorena Soleimani
skatcat31 Robert Mennell
How to contribute
Do you have a cool idea for a new snippet? Maybe some code you use often and is not part of our collection? Contributing to 30 seconds of code is as simple as 1,2,3,4!
1
Create
Start by creating a snippet, according to the snippet template. Make sure to follow these simple guidelines:
  • Your snippet title must be unique and the same as the name of the implemented function.
  • Use the snippet description to explain what your snippet does and how it works.
  • Try to keep the snippet's code short and to the point. Use modern techniques and features.
  • Remember to provide an example of how your snippet works.
  • Your snippet should solve a real-world problem, no matter how simple.
  • Never modify README.md or any of the HTML files.
2
Tag
Run npm run tagger from your terminal, then open the tag_database file and tag your snippet appropriately. Multitagging is also supported, just make sure the first tag you specify is on of the major tags and the one that is most relevant to the implemneted function.
3
Test
You can optionally test your snippet to make our job easier. Simply run npm run tester to generate the test files for your snippet. Find the related folder for you snippet under the test directory and write some tests. Remember to run npm run tester again to make sure your tests are passing.
4
Pull request
If you have done everything mentioned above, you should now have an awesome snippet to add to our collection. Simply start a pull request and follow the guidelines provided. Remember to only submit one snippet per pull request, so that we can quickly evaluate and merge your code into the collection.
If you need additional pointers about writing a snippet, be sure to read the complete contribution guidelines.

30 seconds of code
logo 30 seconds of code
Curated collection of useful JavaScript snippets
that you can understand in 30 seconds or less.
304
snippets
118
contributors
3236
commits
20104
stars
Our philosophy
The core goal of 30 seconds of code is to provide a quality resource for beginner and advanced JavaScript developers alike. We want to help improve the JavaScript ecosystem, by lowering the barrier of entry for newcomers and help seasoned veterans pick up new tricks and remember old ones. In order to achieve this, we have collected hundreds of snippets that can be of use in a wide range of situations. We welcome new contributors and we like fresh ideas, as long as the code is short and easy to grasp in about 30 seconds. The only catch, if you may, is that many of our snippets are not perfectly suited for large, enterprise applications and they might not be deemed production-ready.

In order for 30 seconds of code to be as accessible and useful as possible, all of the snippets in the collection are licensed under the CC0-1.0 License, meaning they are absolutely free to use in any project you like. If you like what we do, you can always credit us, but that is not mandatory.

Today's picks
Our sophisticated robot helpers pick new snippets from our collection daily, so that you can discover new snippets to enhance your projects:
 
isNumber
Checks if the given argument is a number.
Use typeof to check if a value is classified as a number primitive.
const isNumber = val => typeof val === 'number';
-
isNumber('1'); // false
-isNumber(1); // true
-
matchesWith
Compares two objects to determine if the first one contains equivalent property values to the second one, based on a provided function.
Use Object.keys(source) to get all the keys of the second object, then Array.every(), Object.hasOwnProperty() and the provided function to determine if all keys exist in the first object and have equivalent values. If no function is provided, the values will be compared using the equality operator.
const matchesWith = (obj, source, fn) =>
-  Object.keys(source).every(
-    key =>
-      obj.hasOwnProperty(key) && fn
-        ? fn(obj[key], source[key], key, obj, source)
-        : obj[key] == source[key]
-  );
-
const isGreeting = val => /^h(?:i|ello)$/.test(val);
-matchesWith(
-  { greeting: 'hello' },
-  { greeting: 'hi' },
-  (oV, sV) => isGreeting(oV) && isGreeting(sV)
-); // true
-
setStyle
Sets the value of a CSS rule for the specified element.
Use element.style to set the value of the CSS rule for the specified element to val.
const setStyle = (el, ruleName, val) => (el.style[ruleName] = val);
-
setStyle(document.querySelector('p'), 'font-size', '20px'); // The first <p> element on the page will have a font-size of 20px
+30 seconds of code
logo 30 seconds of code
Curated collection of useful JavaScript snippets
that you can understand in 30 seconds or less.
304
snippets
118
contributors
3237
commits
20109
stars
Our philosophy
The core goal of 30 seconds of code is to provide a quality resource for beginner and advanced JavaScript developers alike. We want to help improve the JavaScript ecosystem, by lowering the barrier of entry for newcomers and help seasoned veterans pick up new tricks and remember old ones. In order to achieve this, we have collected hundreds of snippets that can be of use in a wide range of situations. We welcome new contributors and we like fresh ideas, as long as the code is short and easy to grasp in about 30 seconds. The only catch, if you may, is that many of our snippets are not perfectly suited for large, enterprise applications and they might not be deemed production-ready.

In order for 30 seconds of code to be as accessible and useful as possible, all of the snippets in the collection are licensed under the CC0-1.0 License, meaning they are absolutely free to use in any project you like. If you like what we do, you can always credit us, but that is not mandatory.

Today's picks
Our sophisticated robot helpers pick new snippets from our collection daily, so that you can discover new snippets to enhance your projects:
 
binomialCoefficient
Evaluates the binomial coefficient of two integers n and k.
Use Number.isNaN() to check if any of the two values is NaN. Check if k is less than 0, greater than or equal to n, equal to 1 or n - 1 and return the appropriate result. Check if n - k is less than k and switch their values accordingly. Loop from 2 through k and calculate the binomial coefficient. Use Math.round() to account for rounding errors in the calculation.
const binomialCoefficient = (n, k) => {
+  if (Number.isNaN(n) || Number.isNaN(k)) return NaN;
+  if (k < 0 || k > n) return 0;
+  if (k === 0 || k === n) return 1;
+  if (k === 1 || k === n - 1) return n;
+  if (n - k < k) k = n - k;
+  let res = n;
+  for (let j = 2; j <= k; j++) res *= (n - j + 1) / j;
+  return Math.round(res);
+};
+
binomialCoefficient(8, 2); // 28
+
isEmpty
Returns true if the a value is an empty object, collection, map or set, has no enumerable properties or is any type that is not considered a collection.
Check if the provided value is null or if its length is equal to 0.
const isEmpty = val => val == null || !(Object.keys(val) || val).length;
+
isEmpty(new Map()); // true
+isEmpty(new Set()); // true
+isEmpty([]); // true
+isEmpty({}); // true
+isEmpty(''); // true
+isEmpty([1, 2]); // false
+isEmpty({ a: 1, b: 2 }); // false
+isEmpty('text'); // false
+isEmpty(123); // true - type is not considered a collection
+isEmpty(true); // true - type is not considered a collection
+
stripHTMLTags
Removes HTML/XML tags from string.
Use a regular expression to remove HTML/XML tags from a string.
const stripHTMLTags = str => str.replace(/<[^>]*>/g, '');
+
stripHTMLTags('<p><em>lorem</em> <strong>ipsum</strong></p>'); // 'lorem ipsum'
 

Getting started

Related projects
The idea behind 30 seconds of code has inspired some people to create similar collections in other programming languages and environments. Here are the ones we like the most:

Top contributors
chalarangelo Angelos Chalaris
fejes713 Stefan Feješ
flxwu Felix Wu
atomiks atomiks
kingdavidmartins King David Martins
kriadmin Rohit Tanwar
iamsoorena Soorena Soleimani
skatcat31 Robert Mennell
How to contribute
Do you have a cool idea for a new snippet? Maybe some code you use often and is not part of our collection? Contributing to 30 seconds of code is as simple as 1,2,3,4!
1
Create
Start by creating a snippet, according to the snippet template. Make sure to follow these simple guidelines:
  • Your snippet title must be unique and the same as the name of the implemented function.
  • Use the snippet description to explain what your snippet does and how it works.
  • Try to keep the snippet's code short and to the point. Use modern techniques and features.
  • Remember to provide an example of how your snippet works.
  • Your snippet should solve a real-world problem, no matter how simple.
  • Never modify README.md or any of the HTML files.
2
Tag
Run npm run tagger from your terminal, then open the tag_database file and tag your snippet appropriately. Multitagging is also supported, just make sure the first tag you specify is on of the major tags and the one that is most relevant to the implemneted function.
3
Test
You can optionally test your snippet to make our job easier. Simply run npm run tester to generate the test files for your snippet. Find the related folder for you snippet under the test directory and write some tests. Remember to run npm run tester again to make sure your tests are passing.
4
Pull request
If you have done everything mentioned above, you should now have an awesome snippet to add to our collection. Simply start a pull request and follow the guidelines provided. Remember to only submit one snippet per pull request, so that we can quickly evaluate and merge your code into the collection.
If you need additional pointers about writing a snippet, be sure to read the complete contribution guidelines.

30 seconds of code
logo 30 seconds of code
Curated collection of useful JavaScript snippets
that you can understand in 30 seconds or less.
304
snippets
118
contributors
3237
commits
20109
stars
Our philosophy
The core goal of 30 seconds of code is to provide a quality resource for beginner and advanced JavaScript developers alike. We want to help improve the JavaScript ecosystem, by lowering the barrier of entry for newcomers and help seasoned veterans pick up new tricks and remember old ones. In order to achieve this, we have collected hundreds of snippets that can be of use in a wide range of situations. We welcome new contributors and we like fresh ideas, as long as the code is short and easy to grasp in about 30 seconds. The only catch, if you may, is that many of our snippets are not perfectly suited for large, enterprise applications and they might not be deemed production-ready.

In order for 30 seconds of code to be as accessible and useful as possible, all of the snippets in the collection are licensed under the CC0-1.0 License, meaning they are absolutely free to use in any project you like. If you like what we do, you can always credit us, but that is not mandatory.

Today's picks
Our sophisticated robot helpers pick new snippets from our collection daily, so that you can discover new snippets to enhance your projects:
 
binomialCoefficient
Evaluates the binomial coefficient of two integers n and k.
Use Number.isNaN() to check if any of the two values is NaN. Check if k is less than 0, greater than or equal to n, equal to 1 or n - 1 and return the appropriate result. Check if n - k is less than k and switch their values accordingly. Loop from 2 through k and calculate the binomial coefficient. Use Math.round() to account for rounding errors in the calculation.
const binomialCoefficient = (n, k) => {
-  if (Number.isNaN(n) || Number.isNaN(k)) return NaN;
-  if (k < 0 || k > n) return 0;
-  if (k === 0 || k === n) return 1;
-  if (k === 1 || k === n - 1) return n;
-  if (n - k < k) k = n - k;
-  let res = n;
-  for (let j = 2; j <= k; j++) res *= (n - j + 1) / j;
-  return Math.round(res);
+30 seconds of code
logo 30 seconds of code
Curated collection of useful JavaScript snippets
that you can understand in 30 seconds or less.
304
snippets
118
contributors
3238
commits
20125
stars
Our philosophy
The core goal of 30 seconds of code is to provide a quality resource for beginner and advanced JavaScript developers alike. We want to help improve the JavaScript ecosystem, by lowering the barrier of entry for newcomers and help seasoned veterans pick up new tricks and remember old ones. In order to achieve this, we have collected hundreds of snippets that can be of use in a wide range of situations. We welcome new contributors and we like fresh ideas, as long as the code is short and easy to grasp in about 30 seconds. The only catch, if you may, is that many of our snippets are not perfectly suited for large, enterprise applications and they might not be deemed production-ready.

In order for 30 seconds of code to be as accessible and useful as possible, all of the snippets in the collection are licensed under the CC0-1.0 License, meaning they are absolutely free to use in any project you like. If you like what we do, you can always credit us, but that is not mandatory.

Today's picks
Our sophisticated robot helpers pick new snippets from our collection daily, so that you can discover new snippets to enhance your projects:
 
hexToRGB
Converts a color code to a rgb() or rgba() string if alpha value is provided.
Use bitwise right-shift operator and mask bits with & (and) operator to convert a hexadecimal color code (with or without prefixed with #) to a string with the RGB values. If it's 3-digit color code, first convert to 6-digit version. If an alpha value is provided alongside 6-digit hex, give rgba() string in return.
const hexToRGB = hex => {
+  let alpha = false,
+    h = hex.slice(hex.startsWith('#') ? 1 : 0);
+  if (h.length === 3) h = [...h].map(x => x + x).join('');
+  else if (h.length === 8) alpha = true;
+  h = parseInt(h, 16);
+  return (
+    'rgb' +
+    (alpha ? 'a' : '') +
+    '(' +
+    (h >>> (alpha ? 24 : 16)) +
+    ', ' +
+    ((h & (alpha ? 0x00ff0000 : 0x00ff00)) >>> (alpha ? 16 : 8)) +
+    ', ' +
+    ((h & (alpha ? 0x0000ff00 : 0x0000ff)) >>> (alpha ? 8 : 0)) +
+    (alpha ? `, ${h & 0x000000ff}` : '') +
+    ')'
+  );
 };
-
binomialCoefficient(8, 2); // 28
-
isEmpty
Returns true if the a value is an empty object, collection, map or set, has no enumerable properties or is any type that is not considered a collection.
Check if the provided value is null or if its length is equal to 0.
const isEmpty = val => val == null || !(Object.keys(val) || val).length;
-
isEmpty(new Map()); // true
-isEmpty(new Set()); // true
-isEmpty([]); // true
-isEmpty({}); // true
-isEmpty(''); // true
-isEmpty([1, 2]); // false
-isEmpty({ a: 1, b: 2 }); // false
-isEmpty('text'); // false
-isEmpty(123); // true - type is not considered a collection
-isEmpty(true); // true - type is not considered a collection
-
stripHTMLTags
Removes HTML/XML tags from string.
Use a regular expression to remove HTML/XML tags from a string.
const stripHTMLTags = str => str.replace(/<[^>]*>/g, '');
-
stripHTMLTags('<p><em>lorem</em> <strong>ipsum</strong></p>'); // 'lorem ipsum'
+
hexToRGB('#27ae60ff'); // 'rgba(39, 174, 96, 255)'
+hexToRGB('27ae60'); // 'rgb(39, 174, 96)'
+hexToRGB('#fff'); // 'rgb(255, 255, 255)'
+
initializeArrayWithValues
Initializes and fills an array with the specified values.
Use Array(n) to create an array of the desired length, fill(v) to fill it with the desired values. You can omit val to use a default value of 0.
const initializeArrayWithValues = (n, val = 0) => Array(n).fill(val);
+
initializeArrayWithValues(5, 2); // [2,2,2,2,2]
+
matchesWith
Compares two objects to determine if the first one contains equivalent property values to the second one, based on a provided function.
Use Object.keys(source) to get all the keys of the second object, then Array.every(), Object.hasOwnProperty() and the provided function to determine if all keys exist in the first object and have equivalent values. If no function is provided, the values will be compared using the equality operator.
const matchesWith = (obj, source, fn) =>
+  Object.keys(source).every(
+    key =>
+      obj.hasOwnProperty(key) && fn
+        ? fn(obj[key], source[key], key, obj, source)
+        : obj[key] == source[key]
+  );
+
const isGreeting = val => /^h(?:i|ello)$/.test(val);
+matchesWith(
+  { greeting: 'hello' },
+  { greeting: 'hi' },
+  (oV, sV) => isGreeting(oV) && isGreeting(sV)
+); // true
 

Getting started

Related projects
The idea behind 30 seconds of code has inspired some people to create similar collections in other programming languages and environments. Here are the ones we like the most:

Top contributors
chalarangelo Angelos Chalaris
fejes713 Stefan Feješ
flxwu Felix Wu
atomiks atomiks
kingdavidmartins King David Martins
kriadmin Rohit Tanwar
iamsoorena Soorena Soleimani
skatcat31 Robert Mennell
How to contribute
Do you have a cool idea for a new snippet? Maybe some code you use often and is not part of our collection? Contributing to 30 seconds of code is as simple as 1,2,3,4!
1
Create
Start by creating a snippet, according to the snippet template. Make sure to follow these simple guidelines:
  • Your snippet title must be unique and the same as the name of the implemented function.
  • Use the snippet description to explain what your snippet does and how it works.
  • Try to keep the snippet's code short and to the point. Use modern techniques and features.
  • Remember to provide an example of how your snippet works.
  • Your snippet should solve a real-world problem, no matter how simple.
  • Never modify README.md or any of the HTML files.
2
Tag
Run npm run tagger from your terminal, then open the tag_database file and tag your snippet appropriately. Multitagging is also supported, just make sure the first tag you specify is on of the major tags and the one that is most relevant to the implemneted function.
3
Test
You can optionally test your snippet to make our job easier. Simply run npm run tester to generate the test files for your snippet. Find the related folder for you snippet under the test directory and write some tests. Remember to run npm run tester again to make sure your tests are passing.
4
Pull request
If you have done everything mentioned above, you should now have an awesome snippet to add to our collection. Simply start a pull request and follow the guidelines provided. Remember to only submit one snippet per pull request, so that we can quickly evaluate and merge your code into the collection.
If you need additional pointers about writing a snippet, be sure to read the complete contribution guidelines.

30 seconds of code
logo 30 seconds of code
Curated collection of useful JavaScript snippets
that you can understand in 30 seconds or less.
304
snippets
118
contributors
3238
commits
20125
stars
Our philosophy
The core goal of 30 seconds of code is to provide a quality resource for beginner and advanced JavaScript developers alike. We want to help improve the JavaScript ecosystem, by lowering the barrier of entry for newcomers and help seasoned veterans pick up new tricks and remember old ones. In order to achieve this, we have collected hundreds of snippets that can be of use in a wide range of situations. We welcome new contributors and we like fresh ideas, as long as the code is short and easy to grasp in about 30 seconds. The only catch, if you may, is that many of our snippets are not perfectly suited for large, enterprise applications and they might not be deemed production-ready.

In order for 30 seconds of code to be as accessible and useful as possible, all of the snippets in the collection are licensed under the CC0-1.0 License, meaning they are absolutely free to use in any project you like. If you like what we do, you can always credit us, but that is not mandatory.

Today's picks
Our sophisticated robot helpers pick new snippets from our collection daily, so that you can discover new snippets to enhance your projects:
 
hexToRGB
Converts a color code to a rgb() or rgba() string if alpha value is provided.
Use bitwise right-shift operator and mask bits with & (and) operator to convert a hexadecimal color code (with or without prefixed with #) to a string with the RGB values. If it's 3-digit color code, first convert to 6-digit version. If an alpha value is provided alongside 6-digit hex, give rgba() string in return.
const hexToRGB = hex => {
+30 seconds of code
logo 30 seconds of code
Curated collection of useful JavaScript snippets
that you can understand in 30 seconds or less.
304
snippets
118
contributors
3239
commits
20158
stars
Our philosophy
The core goal of 30 seconds of code is to provide a quality resource for beginner and advanced JavaScript developers alike. We want to help improve the JavaScript ecosystem, by lowering the barrier of entry for newcomers and help seasoned veterans pick up new tricks and remember old ones. In order to achieve this, we have collected hundreds of snippets that can be of use in a wide range of situations. We welcome new contributors and we like fresh ideas, as long as the code is short and easy to grasp in about 30 seconds. The only catch, if you may, is that many of our snippets are not perfectly suited for large, enterprise applications and they might not be deemed production-ready.

In order for 30 seconds of code to be as accessible and useful as possible, all of the snippets in the collection are licensed under the CC0-1.0 License, meaning they are absolutely free to use in any project you like. If you like what we do, you can always credit us, but that is not mandatory.

Today's picks
Our sophisticated robot helpers pick new snippets from our collection daily, so that you can discover new snippets to enhance your projects:
 
elo
Computes the new ratings between two or more opponents using the Elo rating system. It takes an array of pre-ratings and returns an array containing post-ratings. The array should be ordered from best performer to worst performer (winner -> loser).
Use the exponent ** operator and math operators to compute the expected score (chance of winning). of each opponent and compute the new rating for each. Loop through the ratings, using each permutation to compute the post-Elo rating for each player in a pairwise fashion. Omit the second argument to use the default kFactor of 32.
const elo = ([...ratings], kFactor = 32, selfRating) => {
+  const [a, b] = ratings;
+  const expectedScore = (self, opponent) => 1 / (1 + 10 ** ((opponent - self) / 400));
+  const newRating = (rating, i) =>
+    (selfRating || rating) + kFactor * (i - expectedScore(i ? a : b, i ? b : a));
+  if (ratings.length === 2) {
+    return [newRating(a, 1), newRating(b, 0)];
+  } else {
+    for (let i = 0; i < ratings.length; i++) {
+      let j = i;
+      while (j < ratings.length - 1) {
+        [ratings[i], ratings[j + 1]] = elo([ratings[i], ratings[j + 1]], kFactor);
+        j++;
+      }
+    }
+  }
+  return ratings;
+};
+
// Standard 1v1s
+elo([1200, 1200]); // [1216, 1184]
+elo([1200, 1200], 64); // [1232, 1168]
+// 4 player FFA, all same rank
+elo([1200, 1200, 1200, 1200]).map(Math.round); // [1246, 1215, 1185, 1154]
+/*
+For teams, each rating can adjusted based on own team's average rating vs.
+average rating of opposing team, with the score being added to their
+own individual rating by supplying it as the third argument.
+*/
+
hexToRGB
Converts a color code to a rgb() or rgba() string if alpha value is provided.
Use bitwise right-shift operator and mask bits with & (and) operator to convert a hexadecimal color code (with or without prefixed with #) to a string with the RGB values. If it's 3-digit color code, first convert to 6-digit version. If an alpha value is provided alongside 6-digit hex, give rgba() string in return.
const hexToRGB = hex => {
   let alpha = false,
     h = hex.slice(hex.startsWith('#') ? 1 : 0);
   if (h.length === 3) h = [...h].map(x => x + x).join('');
@@ -20,24 +48,18 @@
 
hexToRGB('#27ae60ff'); // 'rgba(39, 174, 96, 255)'
 hexToRGB('27ae60'); // 'rgb(39, 174, 96)'
 hexToRGB('#fff'); // 'rgb(255, 255, 255)'
-
initializeArrayWithValues
Initializes and fills an array with the specified values.
Use Array(n) to create an array of the desired length, fill(v) to fill it with the desired values. You can omit val to use a default value of 0.
const initializeArrayWithValues = (n, val = 0) => Array(n).fill(val);
-
initializeArrayWithValues(5, 2); // [2,2,2,2,2]
-
matchesWith
Compares two objects to determine if the first one contains equivalent property values to the second one, based on a provided function.
Use Object.keys(source) to get all the keys of the second object, then Array.every(), Object.hasOwnProperty() and the provided function to determine if all keys exist in the first object and have equivalent values. If no function is provided, the values will be compared using the equality operator.
const matchesWith = (obj, source, fn) =>
-  Object.keys(source).every(
-    key =>
-      obj.hasOwnProperty(key) && fn
-        ? fn(obj[key], source[key], key, obj, source)
-        : obj[key] == source[key]
-  );
-
const isGreeting = val => /^h(?:i|ello)$/.test(val);
-matchesWith(
-  { greeting: 'hello' },
-  { greeting: 'hi' },
-  (oV, sV) => isGreeting(oV) && isGreeting(sV)
-); // true
+
invertKeyValues
Inverts the key-value pairs of an object, without mutating it. The corresponding inverted value of each inverted key is an array of keys responsible for generating the inverted value. If a function is supplied, it is applied to each inverted key.
Use Object.keys() and Array.reduce() to invert the key-value pairs of an object and apply the function provided (if any). Omit the second argument, fn, to get the inverted keys without applying a function to them.
const invertKeyValues = (obj, fn) =>
+  Object.keys(obj).reduce((acc, key) => {
+    const val = fn ? fn(obj[key]) : obj[key];
+    acc[val] = acc[val] || [];
+    acc[val].push(key);
+    return acc;
+  }, {});
+
invertKeyValues({ a: 1, b: 2, c: 1 }); // { 1: [ 'a', 'c' ], 2: [ 'b' ] }
+invertKeyValues({ a: 1, b: 2, c: 1 }, value => 'group' + value); // { group1: [ 'a', 'c' ], group2: [ 'b' ] }
 

Getting started

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1
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2
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3
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4
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