30 seconds of code

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

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Contents

• Anagrams of string (with duplicates)
• Average of array of numbers
• Capitalize first letter of every word
• Capitalize first letter
• Check for palindrome
• Count occurrences of a value in array
• Current URL
• Curry
• Deep flatten array
• Difference between arrays
• Distance between two points
• Divisible by number
• Escape regular expression
• Even or odd number
• Factorial
• Fibonacci array generator
• Filter out non uniqe values in an array
• Flatten array
• Get max value from array
• Get min value from array
• Get native type of value
• Get scroll position
• Greatest common divisor (GCD)
• Head of list
• Initial of list
• Initialize array with range
• Initialize array with values
• Last of list
• Measure time taken by function
• Object from key value pairs
• Pipe
• Powerset
• Random integer in range
• Random number in range
• Randomize order of array
• Redirect to url
• Reverse a string
• RGB to hexadecimal
• Scroll to top
• Shuffle array values
• Similarity between arrays
• Sort characters in string (alphabetical)
• Sum of array of numbers
• Swap values of two variables
• Tail of list
• Unique values of array
• URL parameters
• UUID generator
• Validate number
• Value or default

Anagrams of string (with duplicates)

Use recursion. For each letter in the given string, create all the partial anagrams for the rest of its letters. Use map() to combine the letter with each partial anagram, then reduce() to combine all anagrams in one array. Base cases are for string length equal to 2 or 1.

const anagrams = str => {
  if(str.length <= 2)  return str.length === 2 ? [str, str[1] + str[0]] : [str];
  return str.split('').reduce( (acc, letter, i) => {
    anagrams(str.slice(0, i) + str.slice(i + 1)).map( val => acc.push(letter + val) );
    return acc;
  }, []);
}
// anagrams('abc') -> ['abc','acb','bac','bca','cab','cba']

Average of array of numbers

Use reduce() to add each value to an accumulator, initialized with a value of 0, divide by the length of the array.

const average = arr =>
  arr.reduce( (acc , val) => acc + val, 0) / arr.length;
// average([1,2,3]) -> 2

Capitalize first letter of every word

Use replace() to match the first character of each word and toUpperCase() to capitalize it.

const capitalizeEveryWord = str => str.replace(/\b[a-z]/g, char => char.toUpperCase());
// capitalizeEveryWord('hello world!') -> 'Hello World!'

Capitalize first letter

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.

const capitalize = (str, lowerRest = false) =>
  str.slice(0, 1).toUpperCase() + (lowerRest? str.slice(1).toLowerCase() : str.slice(1));
// capitalize('myName', true) -> 'Myname'

Check for palindrome

Convert string toLowerCase() and use replace() to remove non-alphanumeric characters from it. Then, split('') into individual characters, reverse(), join('') and compare to the original, unreversed string, after converting it tolowerCase().

const palindrome = str =>
  str.toLowerCase().replace(/[\W_]/g,'').split('').reverse().join('') === str.toLowerCase().replace(/[\W_]/g,'');
// palindrome('taco cat') -> true

Count occurrences of a value in array

Use reduce() to increment a counter each time you encounter the specific value inside the array.

const countOccurrences = (arr, value) => arr.reduce((a, v) => v === value ? a + 1 : a + 0, 0);
// countOccurrences([1,1,2,1,2,3], 1) -> 3

Current URL

Use window.location.href to get current URL.

const currentUrl = _ => window.location.href;
// currentUrl() -> 'https://google.com'

Curry

Use recursion. If the number of provided arguments (args) is sufficient, call the passed function f. Otherwise return a curried function f that expects the rest of the arguments.

const curry = f =>
  (...args) =>
    args.length >= f.length ? f(...args) : (...otherArgs) => curry(f)(...args, ...otherArgs);
// curry(Math.pow)(2)(10) -> 1024

Deep flatten array

Use recursion. Use reduce() to get all elements that are not arrays, flatten each element that is an array.

const deepFlatten = arr =>
  arr.reduce( (a, v) => a.concat( Array.isArray(v) ? deepFlatten(v) : v ), []);
// deepFlatten([1,[2],[[3],4],5]) -> [1,2,3,4,5]

Difference between arrays

Use filter() to remove values that are part of values, determined using includes().

const difference = (arr, values) => arr.filter(v => !values.includes(v));
// difference([1,2,3], [1,2]) -> [3]

Distance between two points

Use Math.hypot() to calculate the Euclidean distance between two points.

const distance = (x0, y0, x1, y1) => Math.hypot(x1 - x0, y1 - y0);
// distance(1,1, 2,3) -> 2.23606797749979

Divisible by number

Use the modulo operator (%) to check if the remainder is equal to 0.

const isDivisible = (dividend, divisor) => dividend % divisor === 0;
// isDivisible(6,3) -> true

Escape regular expression

Use replace() to escape special characters.

const escapeRegExp = str => str.replace(/[.*+?^${}()|[\]\\]/g, '\\$&');
// escapeRegExp('(test)') -> \\(test\\)

Even or odd number

Use Math.abs() to extend logic to negative numbers, check using the modulo (%) operator. Return true if the number is even, false if the number is odd.

const isEven = num => Math.abs(num) % 2 === 0;
// isEven(3) -> false

Factorial

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.

const factorial = n => n <= 1 ? 1 : n * factorial(n - 1);
// factorial(6) -> 720

Fibonacci array generator

Create an empty array of the specific length, initializing the first two values (0 and 1). Use Array.reduce() to add values into the array, using the sum of the last two values, except for the first two.

const fibonacci = n => 
  Array(n).fill(0).reduce((acc, val, i) => acc.concat(i > 1 ? acc[i - 1] + acc[i - 2] : i),[]);
// fibonacci(5) -> [0,1,1,2,3]

Filter out non-unique values in an array

Use Array.filter() for an array containing only the unique values.

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 reduce() to get all elements inside the array and concat() to flatten them.

const flatten = arr => arr.reduce( (a, v) => a.concat(v), []);
// flatten([1,[2],3,4]) -> [1,2,3,4]

Get max value from array

Use Math.max() combined with the spread operator (...) to get the maximum value in the array.

const arrayMax = arr => Math.max(...arr);
// arrayMax([10, 1, 5]) -> 10

Get min value from array

Use Math.min() combined with the spread operator (...) to get the minimum value in the array.

const arrayMin = arr => Math.min(...arr);
// arrayMin([10, 1, 5]) -> 1

Get native type of value

Returns lower-cased constructor name of value, "undefined" or "null" if value is undefined or null

const getType = v =>
  v === undefined ? "undefined" : v === null ? "null" : v.constructor.name.toLowerCase(); 
// getType(new Set([1,2,3])) -> "set"

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.

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. 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.

const gcd = (x , y) => !y ? x : gcd(y, x % y);
// gcd (8, 36) -> 4

Head of list

Return arr[0].

const head = arr => arr[0];
// head([1,2,3]) -> 1

Initial of list

Return arr.slice(0,-1).

const initial = arr => arr.slice(0,-1);
// initial([1,2,3]) -> [1,2]

Initialize array with range

Use Array(end-start) to create an array of the desired length, map() to fill with the desired values in a range. You can omit start to use a default value of 0.

const initializeArrayRange = (end, start = 0) =>
  Array.apply(null, Array(end-start)).map( (v,i) => i + start );
// initializeArrayRange(5) -> [0,1,2,3,4]

Initialize array with values

Use Array(n) to create an array of the desired length, fill(v) to fill it with the desired values. You can omit value to use a default value of 0.

const initializeArray = (n, value = 0) => Array(n).fill(value);
// initializeArray(5, 2) -> [2,2,2,2,2]

Last of list

Return arr.slice(-1)[0].

const last = arr => arr.slice(-1)[0];
// last([1,2,3]) -> 3

Measure time taken by function

Use performance.now() to get start and end time for the function, console.log() the time taken. First argument is the function name, subsequent arguments are passed to the function.

const timeTaken = (func,...args) => {
  var t0 = performance.now(), r = func(...args);
  console.log(performance.now() - t0);
  return r;
}
// timeTaken(Math.pow, 2, 10) -> 1024 (0.010000000009313226 logged in console)

Object from key-value pairs

Use Array.reduce() to create and combine key-value pairs.

const objectFromPairs = arr => arr.reduce((a,v) => (a[v[0]] = v[1], a), {});
// objectFromPairs([['a',1],['b',2]]) -> {a: 1, b: 2}

Pipe

Use Array.reduce() to pass value through functions.

const pipe = (...funcs) => arg => funcs.reduce((acc, func) => func(acc), arg);
// pipe(btoa, x => x.toUpperCase())("Test") -> "VGVZDA=="

Powerset

Use reduce() combined with map() to iterate over elements and combine into an array containing all combinations.

const powerset = arr =>
  arr.reduce( (a,v) => a.concat(a.map( r => [v].concat(r) )), [[]]);
// powerset([1,2]) -> [[], [1], [2], [2,1]]

Random integer in range

Use Math.random() to generate a random number and map it to the desired range, using Math.floor() to make it an integer.

const randomIntegerInRange = (min, max) => Math.floor(Math.random() * (max - min + 1)) + min;
// randomIntegerInRange(0, 5) -> 2

Random number in range

Use Math.random() to generate a random value, map it to the desired range using multiplication.

const randomInRange = (min, max) => Math.random() * (max - min) + min;
// randomInRange(2,10) -> 6.0211363285087005

Randomize order of array

Use sort() to reorder elements, utilizing Math.random() to randomize the sorting.

const randomizeOrder = arr => arr.sort( (a,b) => Math.random() >= 0.5 ? -1 : 1);
// randomizeOrder([1,2,3]) -> [1,3,2]

Redirect to URL

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).

const redirect = (url, asLink = true) =>
  asLink ? window.location.href = url : window.location.replace(url);
// redirect('https://google.com')

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('').

const reverseString = str => [...str].reverse().join('');
// reverseString('foobar') -> 'raboof'

RGB to hexadecimal

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.

const rgbToHex = (r, g, b) => ((r << 16) + (g << 8) + b).toString(16).padStart(6, '0');
// rgbToHex(255, 165, 1) -> 'ffa501'

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.requestAnimationFrame() to animate the scrolling.

const scrollToTop = _ => {
  const c = document.documentElement.scrollTop || document.body.scrollTop;
  if(c > 0) {
    window.requestAnimationFrame(scrollToTop);
    window.scrollTo(0, c - c/8);
  }
}
// scrollToTop()

Shuffle array values

Create an array of random values by using Array.map() and Math.random(). Use Array.sort() to sort the elements of the original array based on the random values.

const shuffle = arr => {
  let r = arr.map(Math.random);
  return arr.sort((a,b) => r[a] - r[b]);
}
// shuffle([1,2,3]) -> [2, 1, 3]

Similarity between arrays

Use filter() to remove values that are not part of values, determined using includes().

const similarity = (arr, values) => arr.filter(v => values.includes(v));
// similarity([1,2,3], [1,2,4]) -> [1,2]

Sort characters in string (alphabetical)

Split the string using split(''), sort() utilizing localeCompare(), recombine using join('').

const sortCharactersInString = str =>
  str.split('').sort( (a,b) => a.localeCompare(b) ).join('');
// sortCharactersInString('cabbage') -> 'aabbceg'

Sum of array of numbers

Use reduce() to add each value to an accumulator, initialized with a value of 0.

const sum = arr => arr.reduce( (acc , val) => acc + val, 0);
// sum([1,2,3,4]) -> 10

Swap values of two variables

Use array destructuring to swap values between two variables.

[varA, varB] = [varB, varA];
// [x, y] = [y, x]

Tail of list

Return arr.slice(1) if the array's length is more than 1, otherwise return the whole array.

const tail = arr => arr.length > 1 ? arr.slice(1) : arr;
// tail([1,2,3]) -> [2,3]
// tail([1]) -> [1]

Unique values of array

Use ES6 Set and the ...rest operator to discard all duplicated values.

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.

const getUrlParameters = url =>
  Object.assign(...url.match(/([^?=&]+)(=([^&]*))?/g).map(m => {[f,v] = m.split('='); return {[f]:v}}));
// getUrlParameters('http://url.com/page?name=Adam&surname=Smith') -> {name: 'Adam', surname: 'Smith'}

UUID generator

Use crypto API to generate a UUID, compliant with RFC4122 version 4.

const uuid = _ =>
  ( [1e7]+-1e3+-4e3+-8e3+-1e11 ).replace( /[018]/g, c =>
    (c ^ crypto.getRandomValues(new Uint8Array(1))[0] & 15 >> c / 4).toString(16)
  );
// uuid() -> '7982fcfe-5721-4632-bede-6000885be57d'

Validate number

Use !isNaN in combination with parseFloat() to check if the argument is a number. Use isFinite() to check if the number is finite.

const validateNumber = n => !isNaN(parseFloat(n)) && isFinite(n);
// validateNumber('10') -> true

Value or default

Returns value, or default value if passed value is falsy.

const valueOrDefault = (value, d) => value || d;
// valueOrDefault(NaN, 30) -> 30

Credits

Icons made by Smashicons from www.flaticon.com is licensed by CC 3.0 BY.