Curated collection of useful Javascript snippets that you can understand in 30 seconds or less.
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- Snippets are written in ES6, use the Babel transpiler to ensure backwards-compatibility.
- Anagrams of string (with duplicates)
- Array difference
- Array intersection
- Array union
- Average of array of numbers
- Bottom visible
- Capitalize first letter of every word
- Capitalize first letter
- Chain asynchronous functions
- Check for palindrome
- Chunk array
- Count occurrences of a value in array
- Current URL
- Curry
- Deep flatten array
- Distance between two points
- Divisible by number
- Escape regular expression
- Even or odd number
- Factorial
- Fibonacci array generator
- Filter out non unique 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)
- Hamming distance
- Head of list
- Initial of list
- Initialize array with range
- Initialize array with values
- Last of list
- Measure time taken by function
- Median of array of numbers
- Object from key value pairs
- Object to key value pairs
- Percentile
- Pick
- Pipe
- Powerset
- Promisify
- Random integer in range
- Random number in range
- Randomize order of array
- Redirect to URL
- Reverse a string
- RGB to hexadecimal
- Run promises in series
- 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
- Truncate a string
- Unique values of array
- URL parameters
- UUID generator
- Validate number
- Value or default
Use recursion.
For each letter in the given string, create all the partial anagrams for the rest of its letters.
Use Array.map() to combine the letter with each partial anagram, then Array.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) =>
acc.concat(anagrams(str.slice(0, i) + str.slice(i + 1)).map(val => letter + val)), []);
};
// anagrams('abc') -> ['abc','acb','bac','bca','cab','cba']Create a Set from b, then use Array.filter() on a to only keep values not contained in b.
const difference = (a, b) => { const s = new Set(b); return a.filter(x => !s.has(x)); }
// difference([1,2,3], [1,2]) -> [3]Create a Set from b, then use Array.filter() on a to only keep values contained in b.
const intersection = (a, b) => { const s = new Set(b); return a.filter(x => s.has(x)); }
// intersection([1,2,3], [4,3,2]) -> [2,3]Create a Set with all values of a and b and convert to an array.
const union = (a, b) => Array.from(new Set([...a, ...b]))
// union([1,2,3], [4,3,2]) -> [1,2,3,4]Use Array.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]) -> 2Use scrollY, scrollHeight and clientHeight to determine if the bottom of the page is visible.
const bottomVisible = _ =>
document.documentElement.clientHeight + window.scrollY >= document.documentElement.scrollHeight || document.documentElement.clientHeight;
// bottomVisible() -> trueUse 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!'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'Loop through an array of functions containing asynchronous events, calling next when each asynchronous event has completed.
const chainAsync = fns => { let curr = 0; const next = () => fns[curr++](next); next(); };
/*
chainAsync([
next => { console.log('0 seconds'); setTimeout(next, 1000); },
next => { console.log('1 second'); setTimeout(next, 1000); },
next => { console.log('2 seconds'); }
])
*/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 => {
const s = str.toLowerCase().replace(/[\W_]/g,'');
return s === s.split('').reverse().join('');
}
// palindrome('taco cat') -> trueUse Array.apply() to create a new array, that fits the number of chunks that will be produced.
Use Array.map() to map each element of the new array to a chunk the length of size.
If the original array can't be split evenly, the final chunk will contain the remaining elements.
const chunk = (arr, size) =>
Array.apply(null, {length: Math.ceil(arr.length / size)}).map((v, i) => arr.slice(i * size, i * size + size));
// chunk([1,2,3,4,5], 2) -> [[1,2],[3,4],5]Use Array.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) -> 3Use window.location.href to get current URL.
const currentUrl = _ => window.location.href;
// currentUrl() -> 'https://google.com'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.
If you want to curry a function that accepts a variable number of arguments (a variadic function, e.g. Math.min()), you can optionally pass the number of arguments to the second parameter arity.
const curry = (f, arity = f.length, next) =>
(next = prevArgs =>
nextArg => {
const args = [ ...prevArgs, nextArg ];
return args.length >= arity ? f(...args) : next(args);
}
)([]);
// curry(Math.pow)(2)(10) -> 1024
// curry(Math.min, 3)(10)(50)(2) -> 2Use recursion.
Use Array.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]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) -> 2.23606797749979Use the modulo operator (%) to check if the remainder is equal to 0.
const isDivisible = (dividend, divisor) => dividend % divisor === 0;
// isDivisible(6,3) -> trueUse replace() to escape special characters.
const escapeRegExp = str => str.replace(/[.*+?^${}()|[\]\\]/g, '\\$&');
// escapeRegExp('(test)') -> \\(test\\)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) -> falseUse 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) -> 720Create 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]Use Array.filter() for an array containing only the unique values.
const filterNonUnique = arr => arr.filter(i => arr.indexOf(i) === arr.lastIndexOf(i));
// filterNonUnique([1,2,2,3,4,4,5]) -> [1,3,5]Use Array.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]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]) -> 10Use 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]) -> 1Returns 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"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}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) -> 4Use XOR operator (^) to find the bit difference between the two numbers, convert to binary string using toString(2).
Count and return the number of 1s in the string, using match(/1/g).
const hammingDistance = (num1, num2) =>
((num1 ^ num2).toString(2).match(/1/g) || '').length;
// hammingDistance(2,3) -> 1Return arr[0].
const head = arr => arr[0];
// head([1,2,3]) -> 1Return arr.slice(0,-1).
const initial = arr => arr.slice(0, -1);
// initial([1,2,3]) -> [1,2]Use Array(end-start) to create an array of the desired length, Array.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]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]Return arr.slice(-1)[0].
const last = arr => arr.slice(-1)[0];
// last([1,2,3]) -> 3Use performance.now() to get start and end time for the function, console.log() the time taken.
Pass a callback function as the argument.
const timeTaken = callback => {
const t0 = performance.now(), r = callback();
console.log(performance.now() - t0);
return r;
};
// timeTaken(() => Math.pow(2, 10)) -> 1024 (0.010000000009313226 logged in console)Find the middle of the array, use Array.sort() to sort the values.
Return the number at the midpoint if length is odd, otherwise the average of the two middle numbers.
const median = arr => {
const mid = Math.floor(arr.length / 2), nums = arr.sort((a, b) => a - b);
return arr.length % 2 !== 0 ? nums[mid] : (nums[mid - 1] + nums[mid]) / 2;
};
// median([5,6,50,1,-5]) -> 5
// median([0,10,-2,7]) -> 3.5Use 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}Use Object.keys() and Array.map() to iterate over the object's keys and produce an array with key-value pairs.
const objectToPairs = obj => Object.keys(obj).map(k => [k, obj[k]]);
// objectToPairs({a: 1, b: 2}) -> [['a',1],['b',2]])Use Array.reduce() to calculate how many numbers are below the value and how many are the same value and
apply the percentile formula.
const percentile = (arr, val) =>
100 * arr.reduce((acc,v) => acc + (v < val ? 1 : 0) + (v === val ? 0.5 : 0), 0) / arr.length;
// percentile([1,2,3,4,5,6,7,8,9,10], 6) -> 55Use Array.reduce() to convert the filtered/picked keys back to a object with the corresponding key:value pair if the key exist in the obj.
const pick = (obj, arr) =>
arr.reduce((acc, curr) => (curr in obj && (acc[curr] = obj[curr]), acc), {});
// pick({ 'a': 1, 'b': '2', 'c': 3 }, ['a', 'c']) -> { 'a': 1, 'c': 3 }
// pick(object, ['a', 'c'])['a'] -> 1Use 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=="Use Array.reduce() combined with Array.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]]Use currying to return a function returning a Promise that calls the original function.
Use the ...rest operator to pass in all the parameters.
In Node 8+, you can use util.promisify
const promisify = func =>
(...args) =>
new Promise((resolve, reject) =>
func(...args, (err, result) =>
err ? reject(err) : resolve(result))
);
// const delay = promisify((d, cb) => setTimeout(cb, d))
// delay(2000).then(() => console.log('Hi!')) -> Promise resolves after 2sUse 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) -> 2Use 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) -> 6.0211363285087005Use Array.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]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')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'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'Run an array of promises in series using Array.reduce() by creating a promise chain, where each promise returns the next promise when resolved.
const series = ps => ps.reduce((p, next) => p.then(next), Promise.resolve());
// const delay = (d) => new Promise(r => setTimeout(r, d))
// series([() => delay(1000), () => delay(2000)]) -> executes each promise sequentially, taking a total of 3 seconds to completeGet 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()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]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]Split the string using split(''), Array.sort() utilizing localeCompare(), recombine using join('').
const sortCharactersInString = str =>
str.split('').sort((a, b) => a.localeCompare(b)).join('');
// sortCharactersInString('cabbage') -> 'aabbceg'Use Array.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]) -> 10Use array destructuring to swap values between two variables.
[varA, varB] = [varB, varA];
// [x, y] = [y, x]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]Determine if the string's length is greater than num.
Return the string truncated to the desired length, with ... appended to the end or the original string.
const truncate = (str, num) =>
str.length > num ? str.slice(0, num > 3 ? num - 3 : num) + '...' : str;
// truncate('boomerang', 7) -> 'boom...'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]Use match() with an appropriate regular expression to get all key-value pairs, Array.reduce() to map and combine them into a single object.
Pass location.search as the argument to apply to the current url.
const getUrlParameters = url =>
url.match(/([^?=&]+)(=([^&]*))?/g).reduce(
(a, v) => (a[v.slice(0, v.indexOf('='))] = v.slice(v.indexOf('=') + 1), a), {}
);
// getUrlParameters('http://url.com/page?name=Adam&surname=Smith') -> {name: 'Adam', surname: 'Smith'}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'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') -> trueReturns value, or default value if passed value is falsy.
const valueOrDefault = (value, d) => value || d;
// valueOrDefault(NaN, 30) -> 30Icons made by Smashicons from www.flaticon.com is licensed by CC 3.0 BY.