547 lines
16 KiB
Markdown
547 lines
16 KiB
Markdown
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# 30 seconds of code
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> Curated collection of useful Javascript snippets that you can understand in 30 seconds or less.
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- Use <kbd>Ctrl</kbd> + <kbd>F</kbd> or <kbd>command</kbd> + <kbd>F</kbd> to search for a snippet.
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- Contributions welcome, please read [contribution guide](CONTRIBUTING.md).
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## Contents
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* [Anagrams of string (with duplicates)](#anagrams-of-string-with-duplicates)
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* [Average of array of numbers](#average-of-array-of-numbers)
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* [Capitalize first letter of every word](#capitalize-first-letter-of-every-word)
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* [Capitalize first letter](#capitalize-first-letter)
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* [Check for palindrome](#check-for-palindrome)
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* [Count occurrences of a value in array](#count-occurrences-of-a-value-in-array)
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* [Current URL](#current-url)
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* [Curry](#curry)
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* [Deep flatten array](#deep-flatten-array)
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* [Difference between arrays](#difference-between-arrays)
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* [Distance between two points](#distance-between-two-points)
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* [Divisible by number](#divisible-by-number)
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* [Escape regular expression](#escape-regular-expression)
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* [Even or odd number](#even-or-odd-number)
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* [Factorial](#factorial)
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* [Fibonacci array generator](#fibonacci-array-generator)
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* [Filter out non uniqe values in an array](#filter-out-non-uniqe-values-in-an-array)
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* [Flatten array](#flatten-array)
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* [Get max value from array](#get-max-value-from-array)
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* [Get min value from array](#get-min-value-from-array)
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* [Get scroll position](#get-scroll-position)
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* [Greatest common divisor (GCD)](#greatest-common-divisor-gcd)
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* [Head of list](#head-of-list)
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* [Initial of list](#initial-of-list)
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* [Initialize array with range](#initialize-array-with-range)
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* [Initialize array with values](#initialize-array-with-values)
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* [Last of list](#last-of-list)
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* [Measure time taken by function](#measure-time-taken-by-function)
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* [Object from key value pairs](#object-from-key-value-pairs)
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* [Pipe](#pipe)
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* [Powerset](#powerset)
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* [Random number in range](#random-number-in-range)
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* [Randomize order of array](#randomize-order-of-array)
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* [Redirect to url](#redirect-to-url)
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* [Reverse a string](#reverse-a-string)
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* [RGB to hexadecimal](#rgb-to-hexadecimal)
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* [Scroll to top](#scroll-to-top)
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* [Shuffle array values](#shuffle-array-values)
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* [Similarity between arrays](#similarity-between-arrays)
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* [Sort characters in string (alphabetical)](#sort-characters-in-string-alphabetical)
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* [Sum of array of numbers](#sum-of-array-of-numbers)
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* [Swap values of two variables](#swap-values-of-two-variables)
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* [Tail of list](#tail-of-list)
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* [Unique values of array](#unique-values-of-array)
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* [URL parameters](#url-parameters)
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* [UUID generator](#uuid-generator)
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* [Validate number](#validate-number)
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### Anagrams of string (with duplicates)
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Use recursion.
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For each letter in the given string, create all the partial anagrams for the rest of its letters.
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Use `map()` to combine the letter with each partial anagram, then `reduce()` to combine all anagrams in one array.
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Base cases are for string `length` equal to `2` or `1`.
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```js
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const anagrams = str => {
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if(str.length <= 2) return str.length === 2 ? [str, str[1] + str[0]] : [str];
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return str.split('').reduce( (acc, letter, i) => {
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anagrams(str.slice(0, i) + str.slice(i + 1)).map( val => acc.push(letter + val) );
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return acc;
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}, []);
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}
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// anagrams('abc') -> ['abc','acb','bac','bca','cab','cba']
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```
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### Average of array of numbers
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Use `reduce()` to add each value to an accumulator, initialized with a value of `0`, divide by the `length` of the array.
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```js
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const average = arr =>
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arr.reduce( (acc , val) => acc + val, 0) / arr.length;
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// average([1,2,3]) -> 2
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```
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### Capitalize first letter of every word
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Use `replace()` to match the first character of each word and `toUpperCase()` to capitalize it.
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```js
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const capitalizeEveryWord = str => str.replace(/\b[a-z]/g, char => char.toUpperCase());
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// capitalizeEveryWord('hello world!') -> 'Hello World!'
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```
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### Capitalize first letter
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Use `slice(0,1)` and `toUpperCase()` to capitalize first letter, `slice(1)` to get the rest of the string.
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Omit the `lowerRest` parameter to keep the rest of the string intact, or set it to `true` to convert to lower case.
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```js
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const capitalize = (str, lowerRest = false) =>
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str.slice(0, 1).toUpperCase() + (lowerRest? str.slice(1).toLowerCase() : str.slice(1));
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// capitalize('myName', true) -> 'Myname'
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```
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### Check for palindrome
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Convert string `toLowerCase()` and use `replace()` to remove non-alphanumeric characters from it.
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Then, `split('')` into individual characters, `reverse()`, `join('')` and compare to the original, unreversed string, after converting it `tolowerCase()`.
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```js
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const palindrome = str =>
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str.toLowerCase().replace(/[\W_]/g,'').split('').reverse().join('') === str.toLowerCase().replace(/[\W_]/g,'');
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// palindrome('taco cat') -> true
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```
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### Count occurrences of a value in array
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Use `reduce()` to increment a counter each time you encounter the specific value inside the array.
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```js
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const countOccurrences = (arr, value) => arr.reduce((a, v) => v === value ? a + 1 : a + 0, 0);
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// countOccurrences([1,1,2,1,2,3], 1) -> 3
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```
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### Current URL
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Use `window.location.href` to get current URL.
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```js
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const currentUrl = _ => window.location.href;
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// currentUrl() -> 'https://google.com'
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```
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### Curry
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Use recursion.
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If the number of provided arguments (`args`) is sufficient, call the passed function `f`.
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Otherwise return a curried function `f` that expects the rest of the arguments.
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```js
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const curry = f =>
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(...args) =>
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args.length >= f.length ? f(...args) : (...otherArgs) => curry(f)(...args, ...otherArgs);
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// curry(Math.pow)(2)(10) -> 1024
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```
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### Deep flatten array
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Use recursion.
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Use `reduce()` to get all elements that are not arrays, flatten each element that is an array.
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```js
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const deepFlatten = arr =>
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arr.reduce( (a, v) => a.concat( Array.isArray(v) ? flatten(v) : v ), []);
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// deepFlatten([1,[2],[[3],4],5]) -> [1,2,3,4,5]
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```
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### Difference between arrays
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Use `filter()` to remove values that are part of `values`, determined using `includes()`.
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```js
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const difference = (arr, values) => arr.filter(v => !values.includes(v));
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// difference([1,2,3], [1,2]) -> [3]
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```
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### Distance between two points
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Use `Math.hypot()` to calculate the Euclidean distance between two points.
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```js
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const distance = (x0, y0, x1, y1) => Math.hypot(x1 - x0, y1 - y0);
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// distance(1,1, 2,3) -> 2.23606797749979
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```
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### Divisible by number
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Use the modulo operator (`%`) to check if the remainder is equal to `0`.
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```js
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const isDivisible = (dividend, divisor) => dividend % divisor === 0;
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// isDivisible(6,3) -> true
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```
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### Escape regular expression
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Use `replace()` to escape special characters.
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```js
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const escapeRegExp = str => str.replace(/[.*+?^${}()|[\]\\]/g, '\\$&');
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// escapeRegExp('(test)') -> \\(test\\)
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```
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### Even or odd number
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Use `Math.abs()` to extend logic to negative numbers, check using the modulo (`%`) operator.
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Return `true` if the number is even, `false` if the number is odd.
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```js
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const isEven = num => Math.abs(num) % 2 === 0;
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// isEven(3) -> false
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```
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### Factorial
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Use recursion.
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If `n` is less than or equal to `1`, return `1`.
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Otherwise, return the product of `n` and the factorial of `n - 1`.
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```js
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const factorial = n => n <= 1 ? 1 : n * factorial(n - 1);
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// factorial(6) -> 720
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```
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### Fibonacci array generator
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Create an empty array of the specific length, initializing the first two values (`0` and `1`).
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Use `Array.reduce()` to add values into the array, using the sum of the last two values, except for the first two.
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```js
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const fibonacci = n =>
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Array(n).fill(0).reduce((acc, val, i) => acc.concat(i > 1 ? acc[i - 1] + acc[i - 2] : i),[]);
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// fibonacci(5) -> [0,1,1,2,3]
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```
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### Filter out non-unique values in an array
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Use `Array.filter()` for an array containing only the unique values.
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```js
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const unique = arr => arr.filter(i => arr.indexOf(i) === arr.lastIndexOf(i));
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// unique([1,2,2,3,4,4,5]) -> [1,3,5]
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```
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### Flatten array
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Use `reduce()` to get all elements inside the array and `concat()` to flatten them.
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```js
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const flatten = arr => arr.reduce( (a, v) => a.concat(v), []);
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// flatten([1,[2],3,4) -> [1,2,3,4]
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```
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### Get max value from array
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Use `Math.max()` combined with the spread operator (`...`) to get the minimum value in the array.
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```js
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const arrayMax = arr => Math.max(...arr);
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// arrayMax([10, 1, 5]) -> 10
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```
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### Get min value from array
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Use `Math.min()` combined with the spread operator (`...`) to get the minimum value in the array.
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```js
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const arrayMin = arr => Math.min(...arr);
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// arrayMin([10, 1, 5]) -> 1
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```
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### Get scroll position
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Use `pageXOffset` and `pageYOffset` if they are defined, otherwise `scrollLeft` and `scrollTop`.
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You can omit `el` to use a default value of `window`.
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```js
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const getScrollPos = (el = window) =>
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( {x: (el.pageXOffset !== undefined) ? el.pageXOffset : el.scrollLeft,
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y: (el.pageYOffset !== undefined) ? el.pageYOffset : el.scrollTop} );
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// getScrollPos() -> {x: 0, y: 200}
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```
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### Greatest common divisor (GCD)
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Use recursion.
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Base case is when `y` equals `0`. In this case, return `x`.
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Otherwise, return the GCD of `y` and the remainder of the division `x/y`.
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```js
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const gcd = (x , y) => !y ? x : gcd(y, x % y);
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// gcd (8, 36) -> 4
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```
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### Head of list
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Return `arr[0]`.
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```js
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const head = arr => arr[0];
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// head([1,2,3]) -> 1
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```
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### Initial of list
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Return `arr.slice(0,-1)`.
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```js
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const initial = arr => arr.slice(0,-1);
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// initial([1,2,3]) -> [1,2]
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```
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### Initialize array with range
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Use `Array(end-start)` to create an array of the desired length, `map()` to fill with the desired values in a range.
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You can omit `start` to use a default value of `0`.
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```js
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const initializeArrayRange = (end, start = 0) =>
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Array.apply(null, Array(end-start)).map( (v,i) => i + start );
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// initializeArrayRange(5) -> [0,1,2,3,4]
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```
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### Initialize array with values
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Use `Array(n)` to create an array of the desired length, `fill(v)` to fill it with the desired values.
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You can omit `value` to use a default value of `0`.
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```js
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const initializeArray = (n, value = 0) => Array(n).fill(value);
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// initializeArray(5, 2) -> [2,2,2,2,2]
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```
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### Last of list
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Return `arr.slice(-1)[0]`.
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```js
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const last = arr => arr.slice(-1)[0];
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// last([1,2,3]) -> 3
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```
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### Measure time taken by function
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Use `performance.now()` to get start and end time for the function, `console.log()` the time taken.
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First argument is the function name, subsequent arguments are passed to the function.
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```js
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const timeTaken = (func,...args) => {
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var t0 = performance.now(), r = func(...args);
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console.log(performance.now() - t0);
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return r;
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}
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// timeTaken(Math.pow, 2, 10) -> 1024 (0.010000000009313226 logged in console)
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```
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### Object from key-value pairs
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Use `Array.reduce()` to create and combine key-value pairs.
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```js
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const objectFromPairs = arr => arr.reduce((a,v) => (a[v[0]] = v[1], a), {});
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// objectFromPairs([['a',1],['b',2]]) -> {a: 1, b: 2}
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```
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### Pipe
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Use `Array.reduce()` to pass value through functions.
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```js
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const pipe = (...funcs) => arg => funcs.reduce((acc, func) => func(acc), arg);
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// pipe(btoa, x => x.toUpperCase())("Test") -> "VGVZDA=="
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```
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### Powerset
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Use `reduce()` combined with `map()` to iterate over elements and combine into an array containing all combinations.
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```js
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const powerset = arr =>
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arr.reduce( (a,v) => a.concat(a.map( r => [v].concat(r) )), [[]]);
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// powerset([1,2]) -> [[], [1], [2], [2,1]]
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```
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### Random number in range
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Use `Math.random()` to generate a random value, map it to the desired range using multiplication.
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```js
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const randomInRange = (min, max) => Math.random() * (max - min) + min;
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// randomInRange(2,10) -> 6.0211363285087005
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```
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### Randomize order of array
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Use `sort()` to reorder elements, utilizing `Math.random()` to randomize the sorting.
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```js
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const randomizeOrder = arr => arr.sort( (a,b) => Math.random() >= 0.5 ? -1 : 1);
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// randomizeOrder([1,2,3]) -> [1,3,2]
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```
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### Redirect to URL
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Use `window.location.href` or `window.location.replace()` to redirect to `url`.
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Pass a second argument to simulate a link click (`true` - default) or an HTTP redirect (`false`).
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```js
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const redirect = (url, asLink = true) =>
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asLink ? window.location.href = url : window.location.replace(url);
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// redirect('https://google.com')
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```
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### Reverse a string
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Use array destructuring and `Array.reverse()` to reverse the order of the characters in the string.
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Combine characters to get a string using `join('')`.
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```js
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const reverseString = str => [...str].reverse().join('');
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// reverseString('foobar') -> 'raboof'
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```
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### RGB to hexadecimal
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Convert given RGB parameters to hexadecimal string using bitwise left-shift operator (`<<`) and `toString(16)`, then `padStart(6,'0')` to get a 6-digit hexadecimal value.
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```js
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const rgbToHex = (r, g, b) => ((r << 16) + (g << 8) + b).toString(16).padStart(6, '0');
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// rgbToHex(255, 165, 1) -> 'ffa501'
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```
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### Scroll to top
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Get distance from top using `document.documentElement.scrollTop` or `document.body.scrollTop`.
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Scroll by a fraction of the distance from top. Use `window.requestAnimationFrame()` to animate the scrolling.
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```js
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const scrollToTop = _ => {
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const c = document.documentElement.scrollTop || document.body.scrollTop;
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if(c > 0) {
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window.requestAnimationFrame(scrollToTop);
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window.scrollTo(0, c - c/8);
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}
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}
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// scrollToTop()
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```
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### Shuffle array values
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Create an array of random values by using `Array.map()` and `Math.random()`.
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Use `Array.sort()` to sort the elements of the original array based on the random values.
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```js
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const shuffle = arr => {
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let r = arr.map(Math.random);
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return arr.sort((a,b) => r[a] - r[b]);
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}
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// shuffle([1,2,3]) -> [2, 1, 3]
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```
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### Similarity between arrays
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Use `filter()` to remove values that are not part of `values`, determined using `includes()`.
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```js
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const similarity = (arr, values) => arr.filter(v => values.includes(v));
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// similarity([1,2,3], [1,2,4]) -> [1,2]
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```
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### Sort characters in string (alphabetical)
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Split the string using `split('')`, `sort()` utilizing `localeCompare()`, recombine using `join('')`.
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```js
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const sortCharactersInString = str =>
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str.split('').sort( (a,b) => a.localeCompare(b) ).join('');
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// sortCharactersInString('cabbage') -> 'aabbceg'
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```
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### Sum of array of numbers
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Use `reduce()` to add each value to an accumulator, initialized with a value of `0`.
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```js
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const sum = arr => arr.reduce( (acc , val) => acc + val, 0);
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// sum([1,2,3,4]) -> 10
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```
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### Swap values of two variables
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Use array destructuring to swap values between two variables.
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```js
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[varA, varB] = [varB, varA];
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// [x, y] = [y, x]
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```
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### Tail of list
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Return `arr.slice(1)`.
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```js
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const tail = arr => arr.slice(1);
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// tail([1,2,3]) -> [2,3]
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```
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### Unique values of array
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Use ES6 `Set` and the `...rest` operator to discard all duplicated values.
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```js
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const unique = arr => [...new Set(arr)];
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// unique([1,2,2,3,4,4,5]) -> [1,2,3,4,5]
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```
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### URL parameters
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Use `match()` with an appropriate regular expression to get all key-value pairs, `map()` them appropriately.
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Combine all key-value pairs into a single object using `Object.assign()` and the spread operator (`...`).
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Pass `location.search` as the argument to apply to the current `url`.
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```js
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const getUrlParameters = url =>
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Object.assign(...url.match(/([^?=&]+)(=([^&]*))?/g).map(m => {[f,v] = m.split('='); return {[f]:v}}));
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// getUrlParameters('http://url.com/page?name=Adam&surname=Smith') -> {name: 'Adam', surname: 'Smith'}
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```
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### UUID generator
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Use `crypto` API to generate a UUID, compliant with [RFC4122](https://www.ietf.org/rfc/rfc4122.txt) version 4.
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```js
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const uuid = _ =>
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( [1e7]+-1e3+-4e3+-8e3+-1e11 ).replace( /[018]/g, c =>
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(c ^ crypto.getRandomValues(new Uint8Array(1))[0] & 15 >> c / 4).toString(16)
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);
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// uuid() -> '7982fcfe-5721-4632-bede-6000885be57d'
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```
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### Validate number
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Use `!isNaN` in combination with `parseFloat()` to check if the argument is a number.
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Use `isFinite()` to check if the number is finite.
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```js
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const validateNumber = n => !isNaN(parseFloat(n)) && isFinite(n);
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// validateNumber('10') -> true
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```
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## Credits
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*Icons made by [Smashicons](https://www.flaticon.com/authors/smashicons) from [www.flaticon.com](https://www.flaticon.com/) is licensed by [CC 3.0 BY](http://creativecommons.org/licenses/by/3.0/).*
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