diff --git a/docs/index.html b/docs/index.html index 6e6786630..fab531b43 100644 --- a/docs/index.html +++ b/docs/index.html @@ -1,65 +1,25 @@ -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;
+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
3244
commits
20245
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:
 
initialize2DArray
Initializes a 2D array of given width and height and value.
Use Array.map() to generate h rows where each is a new array of size w initialize with value. If the value is not provided, default to null.
const initialize2DArray = (w, h, val = null) =>
+  Array.from({ length: h }).map(() => Array.from({ length: w }).fill(val));
+
initialize2DArray(2, 2, 0); // [[0,0], [0,0]]
+
intersection
Returns a list of elements that exist in both arrays.
Create a Set from b, then use Array.filter() on a to only keep values contained in b.
const intersection = (a, b) => {
+  const s = new Set(b);
+  return a.filter(x => s.has(x));
 };
-
// 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('');
-  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}` : '') +
-    ')'
-  );
+
intersection([1, 2, 3], [4, 3, 2]); // [2,3]
+
stringPermutations
⚠️ WARNING: This function's execution time increases exponentially with each character. Anything more than 8 to 10 characters will cause your browser to hang as it tries to solve all the different combinations.
Generates all permutations of a string (contains duplicates).
Use recursion. For each letter in the given string, create all the partial permutations for the rest of its letters. Use Array.map() to combine the letter with each partial permutation, then Array.reduce() to combine all permutations in one array. Base cases are for string length equal to 2 or 1.
const stringPermutations = str => {
+  if (str.length <= 2) return str.length === 2 ? [str, str[1] + str[0]] : [str];
+  return str
+    .split('')
+    .reduce(
+      (acc, letter, i) =>
+        acc.concat(stringPermutations(str.slice(0, i) + str.slice(i + 1)).map(val => letter + val)),
+      []
+    );
 };
-
hexToRGB('#27ae60ff'); // 'rgba(39, 174, 96, 255)'
-hexToRGB('27ae60'); // 'rgb(39, 174, 96)'
-hexToRGB('#fff'); // 'rgb(255, 255, 255)'
-
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

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.