100+ JavaScript Snippets: Ultimate Collection of JavaScript Snippets

JavaScript is one of the most popular languages you can learn.

JavaScript is one of the most popular languages you can learn. In this post, you’ll see a list of 100+ beneficial JavaScript snippets that you can learn and use immediately.

JavaScript is one of the most popular languages you can learn. As many people say: “If you’re going to learn just one programming language, go for JavaScript.”

If this sounds compelling to you, here’s a list of 100+ beneficial snippets that you can learn and use immediately.

1. all

This snippet returns true if the predicate function returns true for all elements in a collection and false otherwise. You can omit the second argument fnif you want to use Booleanas a default value.

const all = (arr, fn = Boolean) => arr.every(fn);

all([4, 2, 3], x => x > 1); // true
all([1, 2, 3]); // true

2. allEqual

This snippet checks whether all elements of the array are equal.

const allEqual = arr => arr.every(val => val === arr[0]);

allEqual([1, 2, 3, 4, 5, 6]); // false
allEqual([1, 1, 1, 1]); // true

3. approximatelyEqual

This snippet checks whether two numbers are approximately equal to each other, with a small difference.

const approximatelyEqual = (v1, v2, epsilon = 0.001) => Math.abs(v1 - v2) < epsilon;

approximatelyEqual(Math.PI / 2.0, 1.5708); // true

4. arrayToCSV

This snippet converts the elements to strings with comma-separated values.

const arrayToCSV = (arr, delimiter = ',') =>
  arr.map(v => v.map(x => `"${x}"`).join(delimiter)).join('\n');
  
arrayToCSV([['a', 'b'], ['c', 'd']]); // '"a","b"\n"c","d"'
arrayToCSV([['a', 'b'], ['c', 'd']], ';'); // '"a";"b"\n"c";"d"'```

5. arrayToHtmlList

This snippet converts the elements of an array into <li> tags and appends them to the list of the given ID.

const arrayToHtmlList = (arr, listID) =>
  (el => (
    (el = document.querySelector('#' + listID)),
    (el.innerHTML += arr.map(item => `<li>${item}</li>`).join(''))
  ))();
  
arrayToHtmlList(['item 1', 'item 2'], 'myListID');

6. attempt

This snippet executes a function, returning either the result or the caught error object.

const attempt = (fn, ...args) => {
  try {
    return fn(...args);
  } catch (e) {
    return e instanceof Error ? e : new Error(e);
  }
};
var elements = attempt(function(selector) {
  return document.querySelectorAll(selector);
}, '>_>');
if (elements instanceof Error) elements = []; // elements = []

7. average

This snippet returns the average of two or more numerical values.

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

8. averageBy

This snippet returns the average of an array after initially doing the mapping of each element to a value using a given function.

const averageBy = (arr, fn) =>
  arr.map(typeof fn === 'function' ? fn : val => val[fn]).reduce((acc, val) => acc + val, 0) /
  arr.length;
  
averageBy([{ n: 4 }, { n: 2 }, { n: 8 }, { n: 6 }], o => o.n); // 5
averageBy([{ n: 4 }, { n: 2 }, { n: 8 }, { n: 6 }], 'n'); // 5

9. bifurcate

This snippet splits values into two groups and then puts a truthy element of filterin the first group, and in the second group otherwise.

You can use Array.prototype.reduce()and Array.prototype.push()to add elements to groups based on filter.

const bifurcate = (arr, filter) =>
  arr.reduce((acc, val, i) => (acc[filter[i] ? 0 : 1].push(val), acc), [[], []]);
bifurcate(['beep', 'boop', 'foo', 'bar'], [true, true, false, true]); 
// [ ['beep', 'boop', 'bar'], ['foo'] ]

10. bifurcateBy

This snippet splits values into two groups, based on a predicate function. If the predicate function returns a truthy value, the element will be placed in the first group. Otherwise, it will be placed in the second group.

You can use Array.prototype.reduce()and Array.prototype.push()to add elements to groups, based on the value returned by fnfor each element.

const bifurcateBy = (arr, fn) =>
  arr.reduce((acc, val, i) => (acc[fn(val, i) ? 0 : 1].push(val), acc), [[], []]);
  
bifurcateBy(['beep', 'boop', 'foo', 'bar'], x => x[0] === 'b'); 
// [ ['beep', 'boop', 'bar'], ['foo'] ]

11. bottomVisible

This snippet checks whether the bottom of a page is visible.

const bottomVisible = () =>
  document.documentElement.clientHeight + window.scrollY >=
  (document.documentElement.scrollHeight || document.documentElement.clientHeight);

bottomVisible(); // true

12. byteSize

This snippet returns the length of a string in bytes.

const byteSize = str => new Blob([str]).size;

byteSize('😀'); // 4
byteSize('Hello World'); // 11

13. capitalize

This snippet capitalizes the first letter of a string.

const capitalize = ([first, ...rest]) =>
  first.toUpperCase() + rest.join('');
  
capitalize('fooBar'); // 'FooBar'
capitalize('fooBar', true); // 'Foobar'

14. capitalizeEveryWord

This snippet capitalizes the first letter of every word in a given string.

const capitalizeEveryWord = str => str.replace(/\b[a-z]/g, char => char.toUpperCase());

capitalizeEveryWord('hello world!'); // 'Hello World!'

15. castArray

This snippet converts a non-array value into array.

const castArray = val => (Array.isArray(val) ? val : [val]);

castArray('foo'); // ['foo']
castArray([1]); // [1]

16. compact

This snippet removes false values from an array.

const compact = arr => arr.filter(Boolean);

compact([0, 1, false, 2, '', 3, 'a', 'e' * 23, NaN, 's', 34]); 
// [ 1, 2, 3, 'a', 's', 34 ]

17. countOccurrences

This snippet counts the occurrences of a value in an array.

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

18. Create Directory

This snippet uses existsSync() to check whether a directory exists and then mkdirSync() to create it if it doesn’t.

const fs = require('fs');
const createDirIfNotExists = dir => (!fs.existsSync(dir) ? fs.mkdirSync(dir) : undefined);
createDirIfNotExists('test'); 
// creates the directory 'test', if it doesn't exist

19. currentURL

This snippet returns the current URL.

const currentURL = () => window.location.href;

currentURL(); // 'https://medium.com/@fatosmorina'

20. dayOfYear

This snippet gets the day of the year from a Dateobject.

const dayOfYear = date =>
  Math.floor((date - new Date(date.getFullYear(), 0, 0)) / 1000 / 60 / 60 / 24);

dayOfYear(new Date()); // 272

21. decapitalize

This snippet turns the first letter of a string into lowercase.

const decapitalize = ([first, ...rest]) =>
  first.toLowerCase() + rest.join('')

decapitalize('FooBar'); // 'fooBar'
decapitalize('FooBar'); // 'fooBar'

22. deepFlatten

This snippet flattens an array recursively.

const deepFlatten = arr => [].concat(...arr.map(v => (Array.isArray(v) ? deepFlatten(v) : v)));

deepFlatten([1, [2], [[3], 4], 5]); // [1,2,3,4,5]

23. default

This snippet assigns default values for all properties in an object that are undefined.

const defaults = (obj, ...defs) => Object.assign({}, obj, ...defs.reverse(), obj);

defaults({ a: 1 }, { b: 2 }, { b: 6 }, { a: 3 }); // { a: 1, b: 2 }

24. defer

This snippet delays the execution of a function until the current call stack is cleared.

const defer = (fn, ...args) => setTimeout(fn, 1, ...args);

defer(console.log, 'a'), console.log('b'); // logs 'b' then 'a'

25. degreesToRads

This code snippet can be used to convert a value from degrees to radians.

const degreesToRads = deg => (deg * Math.PI) / 180.0;

degreesToRads(90.0); // ~1.5708

26. difference

This snippet finds the difference between two arrays.

const difference = (a, b) => {
  const s = new Set(b);
  return a.filter(x => !s.has(x));
};

difference([1, 2, 3], [1, 2, 4]); // [3]

27. differenceBy

This method returns the difference between two arrays, after applying a given function to each element of both lists.

const differenceBy = (a, b, fn) => {
  const s = new Set(b.map(fn));
  return a.filter(x => !s.has(fn(x)));
};

differenceBy([2.1, 1.2], [2.3, 3.4], Math.floor); // [1.2]
differenceBy([{ x: 2 }, { x: 1 }], [{ x: 1 }], v => v.x); // [ { x: 2 } ]

28. differenceWith

This snippet removes the values for which the comparator function returns false.

const differenceWith = (arr, val, comp) => arr.filter(a => val.findIndex(b => comp(a, b)) === -1);

differenceWith([1, 1.2, 1.5, 3, 0], [1.9, 3, 0], (a, b) => Math.round(a) === Math.round(b)); 
// [1, 1.2]

29. digitize

This snippet gets a number as input and returns an array of its digits.

const digitize = n => [...`${n}`].map(i => parseInt(i));

digitize(431); // [4, 3, 1]

30. distance

This snippet returns the distance between two points by calculating the Euclidean distance.

const distance = (x0, y0, x1, y1) => Math.hypot(x1 - x0, y1 - y0);

distance(1, 1, 2, 3); // 2.23606797749979

31. Drop Elements

This snippet returns a new array with n elements removed from the left.

const drop = (arr, n = 1) => arr.slice(n);

drop([1, 2, 3]); // [2,3]
drop([1, 2, 3], 2); // [3]
drop([1, 2, 3], 42); // []

32. dropRight

This snippet returns a new array with n elements removed from the right.

const dropRight = (arr, n = 1) => arr.slice(0, -n);

dropRight([1, 2, 3]); // [1,2]
dropRight([1, 2, 3], 2); // [1]
dropRight([1, 2, 3], 42); // []

33. dropRightWhile

This snippet removes elements from the right side of an array until the passed function returns true.

const dropRightWhile = (arr, func) => {
  while (arr.length > 0 && !func(arr[arr.length - 1])) arr = arr.slice(0, -1);
  return arr;
};

dropRightWhile([1, 2, 3, 4], n => n < 3); // [1, 2]

34. dropWhile

This snippet removes elements from an array until the passed function returns true.

const dropWhile = (arr, func) => {
  while (arr.length > 0 && !func(arr[0])) arr = arr.slice(1);
  return arr;
};

dropWhile([1, 2, 3, 4], n => n >= 3); // [3,4]

35. elementContains

This snippet checks whether the parent element contains the child.

const elementContains = (parent, child) => parent !== child && parent.contains(child);

elementContains(document.querySelector('head'), document.querySelector('title')); // true
elementContains(document.querySelector('body'), document.querySelector('body')); // false

36. Filter Duplicate Elements

This snippet removes duplicate values in an array.

const filterNonUnique = arr => arr.filter(i => arr.indexOf(i) === arr.lastIndexOf(i));

filterNonUnique([1, 2, 2, 3, 4, 4, 5]); // [1, 3, 5]

37. findKey

This snippet returns the first key that satisfies a given function.

const findKey = (obj, fn) => Object.keys(obj).find(key => fn(obj[key], key, obj));

findKey(
  {
    barney: { age: 36, active: true },
    fred: { age: 40, active: false },
    pebbles: { age: 1, active: true }
  },
  o => o['active']
); // 'barney'

38. findLast

This snippet returns the last element for which a given function returns a truthy value.

const findLast = (arr, fn) => arr.filter(fn).pop();

findLast([1, 2, 3, 4], n => n % 2 === 1); // 3

39. flatten

This snippet flattens an array up to a specified depth using recursion.

const flatten = (arr, depth = 1) =>
  arr.reduce((a, v) => a.concat(depth > 1 && Array.isArray(v) ? flatten(v, depth - 1) : v), []);

flatten([1, [2], 3, 4]); // [1, 2, 3, 4]
flatten([1, [2, [3, [4, 5], 6], 7], 8], 2); // [1, 2, 3, [4, 5], 6, 7, 8]

40. forEachRight

This snippet executes a function for each element of an array starting from the array’s last element.

const forEachRight = (arr, callback) =>
  arr
    .slice(0)
    .reverse()
    .forEach(callback);
    
forEachRight([1, 2, 3, 4], val => console.log(val)); // '4', '3', '2', '1'

41. forOwn

This snippet iterates on each property of an object and iterates a callback for each one respectively.

const forOwn = (obj, fn) => Object.keys(obj).forEach(key => fn(obj[key], key, obj));
forOwn({ foo: 'bar', a: 1 }, v => console.log(v)); // 'bar', 1

42. functionName

This snippet prints the name of a function into the console.

const functionName = fn => (console.debug(fn.name), fn);

functionName(Math.max); // max (logged in debug channel of console)

43. Get Time From Date

This snippet can be used to get the time from a Dateobject as a string.

const getColonTimeFromDate = date => date.toTimeString().slice(0, 8);

getColonTimeFromDate(new Date()); // "08:38:00"

44. Get Days Between Dates

This snippet can be used to find the difference in days between two dates.

const getDaysDiffBetweenDates = (dateInitial, dateFinal) =>
  (dateFinal - dateInitial) / (1000 * 3600 * 24);
  
getDaysDiffBetweenDates(new Date('2019-01-13'), new Date('2019-01-15')); // 2

45. getStyle

This snippet can be used to get the value of a CSS rule for a particular element.

const getStyle = (el, ruleName) => getComputedStyle(el)[ruleName];

getStyle(document.querySelector('p'), 'font-size'); // '16px'

46. getType

This snippet can be used to get the type of a value.

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

47. hasClass

This snippet checks whether an element has a particular class.

const hasClass = (el, className) => el.classList.contains(className);
hasClass(document.querySelector('p.special'), 'special'); // true

48. head

This snippet returns the head of a list.

const head = arr => arr[0];

head([1, 2, 3]); // 1

49. hide

This snippet can be used to hide all elements specified.

const hide = (...el) => [...el].forEach(e => (e.style.display = 'none'));

hide(document.querySelectorAll('img')); // Hides all <img> elements on the page

50. httpsRedirect

This snippet can be used to redirect from HTTP to HTTPS in a particular domain.

const httpsRedirect = () => {
  if (location.protocol !== 'https:') location.replace('https://' + location.href.split('//')[1]);
};

httpsRedirect(); // If you are on http://mydomain.com, you are redirected to https://mydomain.com

51. indexOfAll

This snippet can be used to get all indexes of a value in an array, which returns an empty array, in case this value is not included in it.

const indexOfAll = (arr, val) => arr.reduce((acc, el, i) => (el === val ? [...acc, i] : acc), []);

indexOfAll([1, 2, 3, 1, 2, 3], 1); // [0,3]
indexOfAll([1, 2, 3], 4); // []

52. initial

This snippet returns all elements of an array except the last one.

const initial = arr => arr.slice(0, -1);

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

53. insertAfter

This snippet can be used to insert an HTML string after the end of a particular element.

const insertAfter = (el, htmlString) => el.insertAdjacentHTML('afterend', htmlString);

insertAfter(document.getElementById('myId'), '<p>after</p>'); // <div id="myId">...</div> <p>after</p>

54. insertBefore

This snippet can be used to insert an HTML string before a particular element.

const insertBefore = (el, htmlString) => el.insertAdjacentHTML('beforebegin', htmlString);

insertBefore(document.getElementById('myId'), '<p>before</p>'); // <p>before</p> <div id="myId">...</div>

55. intersection

This snippet can be used to get an array with elements that are included in two other arrays.

const intersection = (a, b) => {
  const s = new Set(b);
  return a.filter(x => s.has(x));
};

intersection([1, 2, 3], [4, 3, 2]); // [2, 3]

56. intersectionBy

This snippet can be used to return a list of elements that exist in both arrays, after a particular function has been executed to each element of both arrays.

const intersectionBy = (a, b, fn) => {
  const s = new Set(b.map(fn));
  return a.filter(x => s.has(fn(x)));
};

intersectionBy([2.1, 1.2], [2.3, 3.4], Math.floor); // [2.1]

57. intersectionWith

This snippet can be used to return a list of elements that exist in both arrays by using a comparator function.

const intersectionWith = (a, b, comp) => a.filter(x => b.findIndex(y => comp(x, y)) !== -1);

intersectionWith([1, 1.2, 1.5, 3, 0], [1.9, 3, 0, 3.9], (a, b) => Math.round(a) === Math.round(b)); // [1.5, 3, 0]

58. is

This snippet can be used to check if a value is of a particular type.

const is = (type, val) => ![, null].includes(val) && val.constructor === type;

is(Array, [1]); // true
is(ArrayBuffer, new ArrayBuffer()); // true
is(Map, new Map()); // true
is(RegExp, /./g); // true
is(Set, new Set()); // true
is(WeakMap, new WeakMap()); // true
is(WeakSet, new WeakSet()); // true
is(String, ''); // true
is(String, new String('')); // true
is(Number, 1); // true
is(Number, new Number(1)); // true
is(Boolean, true); // true
is(Boolean, new Boolean(true)); // true

59. isAfterDate

This snippet can be used to check whether a date is after another date.

const isAfterDate = (dateA, dateB) => dateA > dateB;

isAfterDate(new Date(2010, 10, 21), new Date(2010, 10, 20)); // true

60. isAnagram

This snippet can be used to check whether a particular string is an anagram with another string.

const isAnagram = (str1, str2) => {
  const normalize = str =>
    str
      .toLowerCase()
      .replace(/[^a-z0-9]/gi, '')
      .split('')
      .sort()
      .join('');
  return normalize(str1) === normalize(str2);
};

isAnagram('iceman', 'cinema'); // true

61. isArrayLike

This snippet can be used to check if a provided argument is iterable like an array.

const isArrayLike = obj => obj != null && typeof obj[Symbol.iterator] === 'function';

isArrayLike(document.querySelectorAll('.className')); // true
isArrayLike('abc'); // true
isArrayLike(null); // false

62. isBeforeDate

This snippet can be used to check whether a date is before another date.

const isBeforeDate = (dateA, dateB) => dateA < dateB;

isBeforeDate(new Date(2010, 10, 20), new Date(2010, 10, 21)); // true

63. isBoolean

This snippet can be used to check whether an argument is a boolean.

const isBoolean = val => typeof val === 'boolean';

isBoolean(null); // false
isBoolean(false); // true

64. isBrowser

This snippet can be used to determine whether the current runtime environment is a browser. This is helpful for avoiding errors when running front-end modules on the server (Node).

const isBrowser = () => ![typeof window, typeof document].includes('undefined');

isBrowser(); // true (browser)
isBrowser(); // false (Node)

65. isBrowserTabFocused

This snippet can be used to determine whether the browser tab is focused.

const isBrowserTabFocused = () => !document.hidden;

isBrowserTabFocused(); // true

66. isLowerCase

This snippet can be used to determine whether a string is lower case.

const isLowerCase = str => str === str.toLowerCase();

isLowerCase('abc'); // true
isLowerCase('a3@$'); // true
isLowerCase('Ab4'); // false

67. isNil

This snippet can be used to check whether a value is null or undefined.

const isNil = val => val === undefined || val === null;

isNil(null); // true
isNil(undefined); // true

68. isNull

This snippet can be used to check whether a value is null.

const isNull = val => val === null;

isNull(null); // true

69. isNumber

This snippet can be used to check whether a provided value is a number.

const isNumber = val => typeof val === 'number';

isNumber('1'); // false
isNumber(1); // true

70. isObject

This snippet can be used to check whether a provided value is an object. It uses the Object constructor to create an object wrapper for the given value.

If it is already an object, then an object type that corresponds to the given value will be returned. Otherwise, a new object will be returned.

const isObject = obj => obj === Object(obj);

isObject([1, 2, 3, 4]); // true
isObject([]); // true
isObject(['Hello!']); // true
isObject({ a: 1 }); // true
isObject({}); // true
isObject(true); // false

71. isObjectLike

This snippet can be used to check if a value is not nulland that its typeof is “object”.

const isObjectLike = val => val !== null && typeof val === 'object';

isObjectLike({}); // true
isObjectLike([1, 2, 3]); // true
isObjectLike(x => x); // false
isObjectLike(null); // false

72. isPlainObject

This snippet checks whether a value is an object created by the Object constructor.

const isPlainObject = val => !!val && typeof val === 'object' && val.constructor === Object;

isPlainObject({ a: 1 }); // true
isPlainObject(new Map()); // false

73. isPromiseLike

This snippet checks whether an object looks like a Promise.

const isPromiseLike = obj =>
  obj !== null &&
  (typeof obj === 'object' || typeof obj === 'function') &&
  typeof obj.then === 'function';
  
isPromiseLike({
  then: function() {
    return '';
  }
}); // true
isPromiseLike(null); // false
isPromiseLike({}); // false

74. isSameDate

This snippet can be used to check whether two dates are equal.

const isSameDate = (dateA, dateB) => dateA.toISOString() === dateB.toISOString();

isSameDate(new Date(2010, 10, 20), new Date(2010, 10, 20)); // true

75. isString

This snippet can be used to check whether an argument is a string.

const isString = val => typeof val === 'string';

isString('10'); // true

76. isSymbol

This snippet can be used to check whether an argument is a symbol.

const isSymbol = val => typeof val === 'symbol';

isSymbol(Symbol('x')); // true

77. isUndefined

This snippet can be used to check whether a value is undefined.

const isUndefined = val => val === undefined;

isUndefined(undefined); // true

78. isUpperCase

This snippet can be used to check whether a string is upper case.

const isUpperCase = str => str === str.toUpperCase();

isUpperCase('ABC'); // true
isLowerCase('[email protected]$'); // true
isLowerCase('aB4'); // false

79. isValidJSON

This snippet can be used to check whether a string is a valid JSON.

const isValidJSON = str => {
  try {
    JSON.parse(str);
    return true;
  } catch (e) {
    return false;
  }
};

isValidJSON('{"name":"Adam","age":20}'); // true
isValidJSON('{"name":"Adam",age:"20"}'); // false
isValidJSON(null); // true

80. last

This snippet returns the last element of an array.

const last = arr => arr[arr.length - 1];

last([1, 2, 3]); // 3

81. matches

This snippet compares two objects to determine if the first one contains the same property values as the second one.

const matches = (obj, source) =>
  Object.keys(source).every(key => obj.hasOwnProperty(key) && obj[key] === source[key]);
  
matches({ age: 25, hair: 'long', beard: true }, { hair: 'long', beard: true }); // true
matches({ hair: 'long', beard: true }, { age: 25, hair: 'long', beard: true }); // false

82. maxDate

This snippet can be used to get the latest date.

const maxDate = (...dates) => new Date(Math.max.apply(null, ...dates));

const array = [
  new Date(2017, 4, 13),
  new Date(2018, 2, 12),
  new Date(2016, 0, 10),
  new Date(2016, 0, 9)
];
maxDate(array); // 2018-03-11T22:00:00.000Z

83. maxN

This snippet returns the n largest elements from a list. If nis greater than or equal to the list’s length, then it will return the original list (sorted in descending order).

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] 	

84. minDate

This snippet can be used to get the earliest date.

const minDate = (...dates) => new Date(Math.min.apply(null, ...dates));

const array = [
  new Date(2017, 4, 13),
  new Date(2018, 2, 12),
  new Date(2016, 0, 10),
  new Date(2016, 0, 9)
];
minDate(array); // 2016-01-08T22:00:00.000Z

85. minN

This snippet returns the n smallest elements from a list. If nis greater than or equal to the list’s length, then it will return the original list (sorted in ascending order).

const minN = (arr, n = 1) => [...arr].sort((a, b) => a - b).slice(0, n);

minN([1, 2, 3]); // [1]
minN([1, 2, 3], 2); // [1,2]

86. negate

This snippet can be used to apply the not operator (!) to a predicate function with its arguments.

const negate = func => (...args) => !func(...args);

[1, 2, 3, 4, 5, 6].filter(negate(n => n % 2 === 0)); // [ 1, 3, 5 ]

87. nodeListToArray

This snippet can be used to convert a nodeList to an array.

const nodeListToArray = nodeList => [...nodeList];

nodeListToArray(document.childNodes); // [ <!DOCTYPE html>, html ]

88. pad

This snippet can be used to pad a string on both sides with a specified character if it is shorter than the specified length.

const pad = (str, length, char = ' ') =>
  str.padStart((str.length + length) / 2, char).padEnd(length, char);
  
pad('cat', 8); // '  cat   '
pad(String(42), 6, '0'); // '004200'
pad('foobar', 3); // 'foobar'

89. radsToDegrees

This snippet can be used to convert an angle from radians to degrees.

const radsToDegrees = rad => (rad * 180.0) / Math.PI;

radsToDegrees(Math.PI / 2); // 90

90. Random Hexadecimal Color Code

This snippet can be used to generate a random hexadecimal color code.

const randomHexColorCode = () => {
  let n = (Math.random() * 0xfffff * 1000000).toString(16);
  return '#' + n.slice(0, 6);
};

randomHexColorCode(); // "#e34155"

91. randomIntArrayInRange

This snippet can be used to generate an array with n random integers in a specified range.

const randomIntArrayInRange = (min, max, n = 1) =>
  Array.from({ length: n }, () => Math.floor(Math.random() * (max - min + 1)) + min);
  
randomIntArrayInRange(12, 35, 10); // [ 34, 14, 27, 17, 30, 27, 20, 26, 21, 14 ]

92. randomIntegerInRange

This snippet can be used to generate a random integer in a specified range.

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

randomIntegerInRange(0, 5); // 3

93. randomNumberInRange

This snippet can be used to return a random number in a specified range.

const randomNumberInRange = (min, max) => Math.random() * (max - min) + min;

randomNumberInRange(2, 10); // 6.0211363285087005

94. readFileLines

This snippet can be used to read a file by getting an array of lines from a file.

const fs = require('fs');
const readFileLines = filename =>
  fs
    .readFileSync(filename)
    .toString('UTF8')
    .split('\n');

let arr = readFileLines('test.txt');
console.log(arr); // ['line1', 'line2', 'line3']

95. Redirect to a URL

This snippet can be used to do a redirect to a specified URL.

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

96. reverse

This snippet can be used to reverse a string.

const reverseString = str => [...str].reverse().join('');

reverseString('foobar'); // 'raboof'

97. round

This snippet can be used to round a number to a specified number of digits.

const round = (n, decimals = 0) => Number(`${Math.round(`${n}e${decimals}`)}e-${decimals}`);

round(1.005, 2); // 1.01

98. runPromisesInSeries

This snippet can be used to run an array of promises in series.

const runPromisesInSeries = ps => ps.reduce((p, next) => p.then(next), Promise.resolve());
const delay = d => new Promise(r => setTimeout(r, d));

runPromisesInSeries([() => delay(1000), () => delay(2000)]); 
// Executes each promise sequentially, taking a total of 3 seconds to complete

99. sample

This snippet can be used to get a random number from an array.

const sample = arr => arr[Math.floor(Math.random() * arr.length)];

sample([3, 7, 9, 11]); // 9

100. sampleSize

This snippet can be used to get nrandom elements from unique positions from an array up to the size of the array. Elements in the array are shuffled using the Fisher-Yates algorithm.

const sampleSize = ([...arr], n = 1) => {
  let m = arr.length;
  while (m) {
    const i = Math.floor(Math.random() * m--);
    [arr[m], arr[i]] = [arr[i], arr[m]];
  }
  return arr.slice(0, n);
};

sampleSize([1, 2, 3], 2); // [3,1]
sampleSize([1, 2, 3], 4); // [2,3,1]

101. scrollToTop

This snippet can be used to do a smooth scroll to the top of the current page.

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

scrollToTop();

102. serializeCookie

This snippet can be used to serialize a cookie name-value pair into a Set-Cookie header string.

const serializeCookie = (name, val) => `${encodeURIComponent(name)}=${encodeURIComponent(val)}`;

serializeCookie('foo', 'bar'); // 'foo=bar'

103. setStyle

This snippet can be used to set the value of a CSS rule for a particular element.

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

104. shallowClone

This snippet can be used to create a shallow clone of an object.

const shallowClone = obj => Object.assign({}, obj);

const a = { x: true, y: 1 };
const b = shallowClone(a); // a !== b

105. show

This snippet can be used to show all the elements specified.

const show = (...el) => [...el].forEach(e => (e.style.display = ''));

show(...document.querySelectorAll('img')); // Shows all <img> elements on the page

106. shuffle

This snippet can be used to order the elements of an array randomly using the Fisher-Yates algorithm.

const shuffle = ([...arr]) => {
  let m = arr.length;
  while (m) {
    const i = Math.floor(Math.random() * m--);
    [arr[m], arr[i]] = [arr[i], arr[m]];
  }
  return arr;
};

const foo = [1, 2, 3];
shuffle(foo); // [2, 3, 1], foo = [1, 2, 3]

107. similarity

This snippet can be used to return an array of elements that appear in two arrays.

https://medium.com/better-programming/127-helpful-javascript-snippets-you-can-learn-in-30-seconds-or-less-part-6-of-6-862a6403d334

108. sleep

This snippet can be used to delay the execution of an asynchronous function by putting it into sleep.

const sleep = ms => new Promise(resolve => setTimeout(resolve, ms));

async function sleepyWork() {
  console.log("I'm going to sleep for 1 second.");
  await sleep(1000);
  console.log('I woke up after 1 second.');
}

109. smoothScroll

This snippet can be used to smoothly scroll the element on which it is called into the visible area of the browser window.

const smoothScroll = element =>
  document.querySelector(element).scrollIntoView({
    behavior: 'smooth'
  });
  
smoothScroll('#fooBar'); // scrolls smoothly to the element with the id fooBar
smoothScroll('.fooBar'); // scrolls smoothly to the first element with a class of fooBar

110. sortCharactersInString

This snippet can be used to alphabetically sort the characters in a string.

const sortCharactersInString = str => [...str].sort((a, b) => a.localeCompare(b)).join('');

sortCharactersInString('cabbage'); // 'aabbceg'

111. splitLines

This snippet can be used to split a multi-line string into an array of lines.

const splitLines = str => str.split(/\r?\n/);

splitLines('This\nis a\nmultiline\nstring.\n'); // ['This', 'is a', 'multiline', 'string.' , '']

112. stripHTMLTags

This snippet can be used 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'

113. sum

This snippet can be used to find the sum of two or more numbers or arrays.

const sum = (...arr) => [...arr].reduce((acc, val) => acc + val, 0);

sum(1, 2, 3, 4); // 10
sum(...[1, 2, 3, 4]); // 10

114. tail

This snippet can be used to get an array with all the elements of an array except for the first one. If the array has only one element, then that an array with that element will be returned instead.

const tail = arr => (arr.length > 1 ? arr.slice(1) : arr);

tail([1, 2, 3]); // [2,3]
tail([1]); // [1]

115. take

This snippet can be used to get an array with nelements removed from the beginning.

const take = (arr, n = 1) => arr.slice(0, n);

take([1, 2, 3], 5); // [1, 2, 3]
take([1, 2, 3], 0); // []

116. takeRight

This snippet can be used to get an array with nelements removed from the end.

const takeRight = (arr, n = 1) => arr.slice(arr.length - n, arr.length);

takeRight([1, 2, 3], 2); // [ 2, 3 ]
takeRight([1, 2, 3]); // [3]

117. timeTaken

This snippet can be used to find out the time it takes to execute a function.

const timeTaken = callback => {
  console.time('timeTaken');
  const r = callback();
  console.timeEnd('timeTaken');
  return r;
};

timeTaken(() => Math.pow(2, 10)); // 1024, (logged): timeTaken: 0.02099609375ms

118. times

This snippet can be used to iterate over a callback ntimes.

const times = (n, fn, context = undefined) => {
  let i = 0;
  while (fn.call(context, i) !== false && ++i < n) {}
};

var output = '';
times(5, i => (output += i));
console.log(output); // 01234

119. toCurrency

This snippet can be used to format a number like a currency.

const toCurrency = (n, curr, LanguageFormat = undefined) =>
  Intl.NumberFormat(LanguageFormat, { style: 'currency', currency: curr }).format(n);
  
toCurrency(123456.789, 'EUR'); // €123,456.79  | currency: Euro | currencyLangFormat: Local
toCurrency(123456.789, 'USD', 'en-us'); // $123,456.79  | currency: US Dollar | currencyLangFormat: English (United States)
toCurrency(123456.789, 'USD', 'fa'); // ۱۲۳٬۴۵۶٫۷۹ ؜$ | currency: US Dollar | currencyLangFormat: Farsi
toCurrency(322342436423.2435, 'JPY'); // ¥322,342,436,423 | currency: Japanese Yen | currencyLangFormat: Local
toCurrency(322342436423.2435, 'JPY', 'fi'); // 322 342 436 423 ¥ | currency: Japanese Yen | currencyLangFormat: Finnish

120. toDecimalMark

This snippet uses the toLocaleString()function to convert float-point arithmetic to the decimal mark form by using a number to make a comma-separated string.

const toDecimalMark = num => num.toLocaleString('en-US');

toDecimalMark(12305030388.9087); // "12,305,030,388.909"

121. toggleClass

This snippet can be used to toggle a class for an element.

const toggleClass = (el, className) => el.classList.toggle(className);

toggleClass(document.querySelector('p.special'), 'special'); // The paragraph will not have the 'special' class anymore

122. tomorrow

This snippet can be used to get a string representation of tomorrow’s date.

const tomorrow = () => {
  let t = new Date();
  t.setDate(t.getDate() + 1);
  return t.toISOString().split('T')[0];
};

tomorrow(); // 2019-09-08 (if current date is 2018-09-08)

123. unfold

This snippet can be used to build an array using an iterator function and an initial seed value.

const unfold = (fn, seed) => {
  let result = [],
    val = [null, seed];
  while ((val = fn(val[1]))) result.push(val[0]);
  return result;
};

var f = n => (n > 50 ? false : [-n, n + 10]);
unfold(f, 10); // [-10, -20, -30, -40, -50]

124. union

This snippet can be used to find the union of two arrays, resulting in an array that has elements that come from both arrays but that do not repeat.

const union = (a, b) => Array.from(new Set([...a, ...b]));

union([1, 2, 3], [4, 3, 2]); // [1,2,3,4]

125. uniqueElements

This snippet uses ES6 Setandthe…restoperator to get every element only once.

const uniqueElements = arr => [...new Set(arr)];

uniqueElements([1, 2, 2, 3, 4, 4, 5]); // [1, 2, 3, 4, 5]

126. validateNumber

This snippet can be used to check whether a value is a number.

const validateNumber = n => !isNaN(parseFloat(n)) && isFinite(n) && Number(n) == n;

validateNumber('10'); // true

127. words

This snippet converts a string into an array of words.

const words = (str, pattern = /[^a-zA-Z-]+/) => str.split(pattern).filter(Boolean);

words('I love javaScript!!'); // ["I", "love", "javaScript"]
words('python, javaScript & coffee'); // ["python", "javaScript", "coffee"]

Synopsis

These snippets were taken from this project in which you can find more JavaScript snippets, and also snippets for other technologies and frameworks.

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