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Merge branch 'master' into patch-1

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Angelos Chalaris
2017-12-12 16:05:55 +02:00
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README.md
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@ -8,11 +8,9 @@
## Contents
* [RGB to hexadecimal](#rgb-to-hexadecimal)
* [URL parameters](#url-parameters)
* [UUID generator](#uuid-generator)
* [Anagrams of string (with duplicates)](#anagrams-of-string-with-duplicates)
* [Average of array of numbers](#average-of-array-of-numbers)
* [Capitalize first letter of every word](#capitalize-first-letter-of-every-word)
* [Capitalize first letter](#capitalize-first-letter)
* [Count occurrences of a value in array](#count-occurrences-of-a-value-in-array)
* [Current URL](#current-url)
@ -23,7 +21,9 @@
* [Even or odd number](#even-or-odd-number)
* [Factorial](#factorial)
* [Fibonacci array generator](#fibonacci-array-generator)
* [Filter out non uniqe values in an array](#filter-out-non-uniqe-values-in-an-array)
* [Flatten array](#flatten-array)
* [Get scroll position](#get-scroll-position)
* [Greatest common divisor (GCD)](#greatest-common-divisor-gcd)
* [Head of list](#head-of-list)
* [Initial of list](#initial-of-list)
@ -36,6 +36,8 @@
* [Random number in range](#random-number-in-range)
* [Randomize order of array](#randomize-order-of-array)
* [Redirect to url](#redirect-to-url)
* [Reverse a string](#reverse-a-string)
* [RGB to hexadecimal](#rgb-to-hexadecimal)
* [Scroll to top](#scroll-to-top)
* [Similarity between arrays](#similarity-between-arrays)
* [Sort characters in string (alphabetical)](#sort-characters-in-string-alphabetical)
@ -43,40 +45,10 @@
* [Swap values of two variables](#swap-values-of-two-variables)
* [Tail of list](#tail-of-list)
* [Unique values of array](#unique-values-of-array)
* [URL parameters](#url-parameters)
* [UUID generator](#uuid-generator)
* [Validate number](#validate-number)
### RGB to hexadecimal
Convert each value to a hexadecimal string, using `toString(16)`, then `padStart(2,'0')` to get a 2-digit hexadecimal value.
Combine values using `join('')`.
```js
var rgbToHex = (r, g, b) =>
[r,g,b].map( v => v.toString(16).padStart(2,'0')).join('');
```
### URL parameters
Use `match()` with an appropriate regular expression to get all key-value pairs, `map()` them appropriately.
Combine all key-value pairs into a single object using `Object.assign()` and the spread operator (`...`).
Pass `location.search` as the argument to apply to the current `url`.
```js
var getUrlParameters = url =>
Object.assign(...url.match(/([^?=&]+)(=([^&]*))?/g).map(m => {[f,v] = m.split('='); return {[f]:v}}));
```
### UUID generator
Use `crypto` API to generate a UUID, compliant with [RFC4122](https://www.ietf.org/rfc/rfc4122.txt) version 4.
```js
var uuid = _ =>
( [1e7]+-1e3+-4e3+-8e3+-1e11 ).replace( /[018]/g, c =>
(c ^ crypto.getRandomValues(new Uint8Array(1))[0] & 15 >> c / 4).toString(16)
)
```
### Anagrams of string (with duplicates)
Use recursion.
@ -85,7 +57,7 @@ Use `map()` to combine the letter with each partial anagram, then `reduce()` to
Base cases are for string `length` equal to `2` or `1`.
```js
var anagrams = s => {
const anagrams = s => {
if(s.length <= 2) return s.length === 2 ? [s, s[1] + s[0]] : [s];
return s.split('').reduce( (a,l,i) => {
anagrams(s.slice(0,i) + s.slice(i+1)).map( v => a.push(l+v) );
@ -99,24 +71,34 @@ var anagrams = s => {
Use `reduce()` to add each value to an accumulator, initialized with a value of `0`, divide by the `length` of the array.
```js
var average = arr =>
const average = arr =>
arr.reduce( (acc , val) => acc + val, 0) / arr.length;
```
### Capitalize first letter of every word
Use `replace()` to match the first character of each word and `toUpperCase()` to capitalize it.
```js
const capitalizeEveryWord = str => str.replace(/\b[a-z]/g, char => char.toUpperCase());
```
### Capitalize first letter
Use `toUpperCase()` to capitalize first letter, `slice(1)` to get the rest of the string.
Use `slice(0,1)` and `toUpperCase()` to capitalize first letter, `slice(1)` to get the rest of the string.
Omit the `lowerRest` parameter to keep the rest of the string intact, or set it to `true` to convert to lower case.
```js
var capitalize = str => str[0].toUpperCase() + str.slice(1);
const capitalize = (str, lowerRest = false) =>
str.slice(0, 1).toUpperCase() + (lowerRest? str.slice(1).toLowerCase() : str.slice(1));
```
### Count occurrences of a value in array
Use `filter()` to create an array containing only the items with the specified value, count them using `length`.
Use `reduce()` to increment a counter each time you encounter the specific value inside the array.
```js
var countOccurrences = (arr, value) => arr.filter(v => v === value).length;
const countOccurrences = (arr, value) => arr.reduce((a, v) => v===value ? a + 1 : a + 0, 0);
```
### Current URL
@ -124,7 +106,7 @@ var countOccurrences = (arr, value) => arr.filter(v => v === value).length;
Use `window.location.href` to get current URL.
```js
var currentUrl = _ => window.location.href;
const currentUrl = _ => window.location.href;
```
### Curry
@ -134,27 +116,25 @@ If the number of provided arguments (`args`) is sufficient, call the passed func
Otherwise return a curried function `f` that expects the rest of the arguments.
```js
var curry = f =>
const curry = f =>
(...args) =>
args.length >= f.length ? f(...args) : (...otherArgs) => curry(f)(...args, ...otherArgs)
```
### Difference between arrays
Use `filter()` to remove values that are part of `values`, determined using `indexOf()`.
Use `filter()` to remove values that are part of `values`, determined using `includes()`.
```js
var difference = (arr, values) =>
arr.filter(v => values.indexOf(v) === -1);
const difference = (arr, values) => arr.filter(v => !values.includes(v));
```
### Distance between two points
Use `Math.pow()` and `Math.sqrt()` to calculate the Euclidean distance between two points.
Use `Math.hypot()` to calculate the Euclidean distance between two points.
```js
var distance = x0, y0, x1, y1 =>
Math.sqrt(Math.pow(x1-x0, 2) + Math.pow(y1 - y0, 2))
const distance = (x0, y0, x1, y1) => Math.hypot(x1 - x0, y1 - y0);
```
### Escape regular expression
@ -162,7 +142,7 @@ var distance = x0, y0, x1, y1 =>
Use `replace()` to escape special characters.
```js
var escapeRegExp = s =>
const escapeRegExp = s =>
s.replace(/[.*+?^${}()|[\]\\]/g, '\\$&');
}
```
@ -173,16 +153,17 @@ Use `Math.abs()` to extend logic to negative numbers, check using the modulo (`%
Return `true` if the number is even, `false` if the number is odd.
```js
var isEven = num => Math.abs(num) % 2 === 0;
const isEven = num => Math.abs(num) % 2 === 0;
```
### Factorial
Create an array of length `n+1`, use `reduce()` to get the product of every value in the given range, utilizing the index of each element.
Use recursion.
If `n` is less than or equal to `1`, return `1`.
Otherwise, return the product of `n` and the factorial of `n - 1`.
```js
var factorial = n =>
Array.apply(null, [1].concat(Array(n))).reduce( (a, _, i) => a * i || 1 , 1);
const factorial = n => n <= 1 ? 1 : n * factorial(n - 1)
```
### Fibonacci array generator
@ -191,7 +172,7 @@ Create an empty array of the specific length, initializing the first two values
Use `reduce()` to add values into the array, using the sum of the last two values, except for the first two.
```js
var fibonacci = n =>
const fibonacci = n =>
Array.apply(null, [0,1].concat(Array(n-2))).reduce(
(acc, val, i) => {
acc.push( i>1 ? acc[i-1]+acc[i-2] : val);
@ -199,16 +180,37 @@ var fibonacci = n =>
},[]);
```
### Filter out non-unique values in an array
Use `Array.filter()` for an array containing only the unique values.
```js
const unique = arr => arr.filter(i => arr.indexOf(i) === arr.lastIndexOf(i));
// unique([1,2,2,3,4,4,5]) -> [1,3,5]
```
### Flatten array
Use recursion.
Use `reduce()` to get all elements that are not arrays, flatten each element that is an array.
```js
var flatten = arr =>
const flatten = arr =>
arr.reduce( (a, v) => a.concat( Array.isArray(v) ? flatten(v) : v ), []);
```
## Get scroll position
Use `pageXOffset` and `pageYOffset` if they are defined, otherwise `scrollLeft` and `scrollTop`.
You can omit `el` to use a default value of `window`.
```js
const getScrollPos = (el = window) =>
( {x: (el.pageXOffset !== undefined) ? el.pageXOffset : el.scrollLeft,
y: (el.pageYOffset !== undefined) ? el.pageYOffset : el.scrollTop} );
// getScrollPos() -> {x: 0, y: 200}
```
### Greatest common divisor (GCD)
Use recursion.
@ -216,7 +218,7 @@ Base case is when `y` equals `0`. In this case, return `x`.
Otherwise, return the GCD of `y` and the remainder of the division `x/y`.
```js
var gcd = (x , y) => !y ? x : gcd(y, x % y);
const gcd = (x , y) => !y ? x : gcd(y, x % y);
```
### Head of list
@ -224,7 +226,7 @@ var gcd = (x , y) => !y ? x : gcd(y, x % y);
Return `arr[0]`.
```js
var head = arr => arr[0];
const head = arr => arr[0];
```
### Initial of list
@ -232,7 +234,7 @@ var head = arr => arr[0];
Return `arr.slice(0,-1)`.
```js
var initial = arr => arr.slice(0,-1);
const initial = arr => arr.slice(0,-1);
```
### Initialize array with range
@ -241,7 +243,7 @@ Use `Array(end-start)` to create an array of the desired length, `map()` to fill
You can omit `start` to use a default value of `0`.
```js
var initializeArrayRange = (end, start = 0) =>
const initializeArrayRange = (end, start = 0) =>
Array.apply(null, Array(end-start)).map( (v,i) => i + start );
```
@ -251,7 +253,7 @@ Use `Array(n)` to create an array of the desired length, `fill(v)` to fill it wi
You can omit `v` to use a default value of `0`.
```js
var initializeArray = (n, v = 0) =>
const initializeArray = (n, v = 0) =>
Array(n).fill(v);
```
@ -260,7 +262,7 @@ var initializeArray = (n, v = 0) =>
Return `arr.slice(-1)[0]`.
```js
var initial = arr => arr.slice(-1)[0];
const last = arr => arr.slice(-1)[0];
```
### Measure time taken by function
@ -269,7 +271,7 @@ Use `performance.now()` to get start and end time for the function, `console.log
First argument is the function name, subsequent arguments are passed to the function.
```js
var timeTaken = (f,...args) => {
const timeTaken = (f,...args) => {
var t0 = performance.now(), r = f(...args);
console.log(performance.now() - t0);
return r;
@ -278,19 +280,18 @@ var timeTaken = (f,...args) => {
### Object from key-value pairs
Use `map()` to create objects for each key-value pair, combine with `Object.assign()`.
Use `Array.reduce()` to create and combine key-value pairs.
```js
var objectFromPairs = arr =>
Object.assign(...arr.map( v => ({ [v[0]] : v[1] })));
const objectFromPairs = arr => arr => arr.reduce((a,b) => { a[b[0]] = b[1]; return a;}, {});
```
### Powerset
Use `reduce()` combined with `map()` to iterate over elements and combine into an array containing all combinations.
Use `reduce()` combined with `map()` to iterate over elements and combine into an array containing all combinations.
```js
var powerset = arr =>
const powerset = arr =>
arr.reduce( (a,v) => a.concat(a.map( r => [v].concat(r) )), [[]]);
```
@ -299,7 +300,7 @@ var powerset = arr =>
Use `Math.random()` to generate a random value, map it to the desired range using multiplication.
```js
var randomInRange = (min, max) => Math.random() * (max - min) + min;
const randomInRange = (min, max) => Math.random() * (max - min) + min;
```
### Randomize order of array
@ -307,7 +308,7 @@ var randomInRange = (min, max) => Math.random() * (max - min) + min;
Use `sort()` to reorder elements, utilizing `Math.random()` to randomize the sorting.
```js
var randomizeOrder = arr => arr.sort( (a,b) => Math.random() >= 0.5 ? -1 : 1)
const randomizeOrder = arr => arr.sort( (a,b) => Math.random() >= 0.5 ? -1 : 1)
```
### Redirect to URL
@ -316,18 +317,37 @@ Use `window.location.href` or `window.location.replace()` to redirect to `url`.
Pass a second argument to simulate a link click (`true` - default) or an HTTP redirect (`false`).
```js
var redirect = (url, asLink = true) =>
const redirect = (url, asLink = true) =>
asLink ? window.location.href = url : window.location.replace(url);
```
### Reverse a string
Use array destructuring and `Array.reverse()` to reverse the order of the characters in the string.
Combine characters to get a string using `join('')`.
```js
const reverseString = str => [...str].reverse().join('');
```
### RGB to hexadecimal
Convert each value to a hexadecimal string, using `toString(16)`, then `padStart(2,'0')` to get a 2-digit hexadecimal value.
Combine values using `join('')`.
```js
const rgbToHex = (r, g, b) =>
[r,g,b].map( v => v.toString(16).padStart(2,'0')).join('');
```
### Scroll to top
Get distance from top using `document.documentElement.scrollTop` or `document.body.scrollTop`.
Scroll by a fraction of the distance from top. Use `window.requestFrame()` to animate the scrolling.
Scroll by a fraction of the distance from top. Use `window.requestAnimationFrame()` to animate the scrolling.
```js
var scrollToTop = _ => {
var c = document.documentElement.scrollTop || document.body.scrollTop;
const scrollToTop = _ => {
const c = document.documentElement.scrollTop || document.body.scrollTop;
if(c > 0) {
window.requestAnimationFrame(scrollToTop);
window.scrollTo(0, c - c/8);
@ -337,11 +357,10 @@ var scrollToTop = _ => {
### Similarity between arrays
Use `filter()` to remove values that are not part of `values`, determined using `indexOf()`.
Use `filter()` to remove values that are not part of `values`, determined using `includes()`.
```js
var difference = (arr, values) =>
arr.filter(v => values.indexOf(v) !== -1);
const difference = (arr, values) => arr.filter(v => values.includes(v));
```
### Sort characters in string (alphabetical)
@ -349,7 +368,7 @@ var difference = (arr, values) =>
Split the string using `split('')`, `sort()` utilizing `localeCompare()`, recombine using `join('')`.
```js
var sortCharactersInString = str =>
const sortCharactersInString = str =>
str.split('').sort( (a,b) => a.localeCompare(b) ).join('');
```
@ -358,7 +377,7 @@ var sortCharactersInString = str =>
Use `reduce()` to add each value to an accumulator, initialized with a value of `0`.
```js
var sum = arr =>
const sum = arr =>
arr.reduce( (acc , val) => acc + val, 0);
```
@ -375,21 +394,38 @@ Use array destructuring to swap values between two variables.
Return `arr.slice(1)`.
```js
var tail = arr => arr.slice(1);
const tail = arr => arr.slice(1);
```
### Unique values of array
Use `reduce()` to accumulate all unique values in an array.
Check if each value has already been added, using `indexOf()` on the accumulator array.
Use ES6 `Set` and the `...rest` operator to discard all duplicated values.
```js
var uniqueValues = arr =>
arr.reduce( (acc, val) => {
if(acc.indexOf(val) === -1)
acc.push(val);
return acc;
}, []);
const unique = arr => [...new Set(arr)];
// unique([1,2,2,3,4,4,5]) -> [1,2,3,4,5]
```
### URL parameters
Use `match()` with an appropriate regular expression to get all key-value pairs, `map()` them appropriately.
Combine all key-value pairs into a single object using `Object.assign()` and the spread operator (`...`).
Pass `location.search` as the argument to apply to the current `url`.
```js
const getUrlParameters = url =>
Object.assign(...url.match(/([^?=&]+)(=([^&]*))?/g).map(m => {[f,v] = m.split('='); return {[f]:v}}));
```
### UUID generator
Use `crypto` API to generate a UUID, compliant with [RFC4122](https://www.ietf.org/rfc/rfc4122.txt) version 4.
```js
const uuid = _ =>
( [1e7]+-1e3+-4e3+-8e3+-1e11 ).replace( /[018]/g, c =>
(c ^ crypto.getRandomValues(new Uint8Array(1))[0] & 15 >> c / 4).toString(16)
)
```
### Validate number
@ -398,7 +434,7 @@ Use `!isNaN` in combination with `parseFloat()` to check if the argument is a nu
Use `isFinite()` to check if the number is finite.
```js
var validateNumber = n => !isNaN(parseFloat(n)) && isFinite(n);
const validateNumber = n => !isNaN(parseFloat(n)) && isFinite(n);
```
## Credits