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.
- You can import these snippets into Alfred 3, using this file.
arrayGcdarrayLcmarrayMaxarrayMinchunkcompactcountOccurrencesdeepFlattendifferencedifferenceWithdistinctValuesOfArraydropElementsdropRighteveryNthfilterNonUniqueflattenflattenDepthgroupByheadinitialinitialize2DArrayinitializeArrayWithRangeinitializeArrayWithValuesintersectionlastmapObjectnthElementpickpullpullAtIndexpullAtValueremovesampleshufflesimilaritysymmetricDifferencetailtaketakeRightunionwithoutzipzipObject
arrayToHtmlListbottomVisiblecurrentURLdetectDeviceTypeelementIsVisibleInViewportgetScrollPositiongetURLParametershttpsRedirectredirectscrollToTop
arrayAveragearraySumclampNumbercollatzdigitizedistancefactorialfibonaccifibonacciCountUntilNumfibonacciUntilNumgcdhammingDistanceinRangeisArmstrongNumberisDivisibleisEvenisPrimelcmmedianpalindromepercentilepowersetprimesrandomIntegerInRangerandomNumberInRangeroundstandardDeviation
anagramscapitalizecapitalizeEveryWordcountVowelsescapeRegExpfromCamelCaserepeatStringreverseStringsortCharactersInStringtoCamelCasetoKebabCasetoSnakeCasetruncateStringwords
coalescecoalesceFactoryextendHexgetTypehexToRGBisArrayisBooleanisFunctionisNumberisStringisSymbolrandomHexColorCodeRGBToHexsdbmtimeTakentoDecimalMarktoOrdinalSuffixUUIDGeneratorvalidateNumber
Given a key and a set of arguments, call them when given a context. Primarily useful in composition.
Use a closure to call a stored key with stored arguments.
const call = (key, ...args) => context => context[ key ](...args);Promise.resolve( [ 1, 2, 3 ] ).then( call('map', x => 2 * x ) ).then( console.log ) //[ 2, 4, 6 ]
const map = call.bind(null, 'map')
Promise.resolve( [ 1, 2, 3 ] ).then( map( x => 2 * x ) ).then( console.log ) //[ 2, 4, 6 ]Changes a function that accepts an array into a variadic function.
Given a function, return a closure that collects all inputs into an array-accepting function.
const collectInto = fn => (...args) => fn(args);const Pall = collectInto( Promise.all.bind(Promise) )
let p1 = Promise.resolve(1)
let p2 = Promise.resolve(2)
let p3 = new Promise((resolve) => setTimeout(resolve,2000,3))
Pall(p1, p2, p3).then(console.log)Flip takes a function as an argument, then makes the first argument the last
Return a closure that takes variadic inputs, and splices the last argument to make it the first argument before applying the rest.
const flip = fn => (...args) => fn(args.pop(), ...args);let a = {name: 'John Smith'}
let b = {}
const mergeFrom = flip(Object.assign)
let mergePerson = mergeFrom.bind(null, a)
mergePerson(b) // == b
b = {}
Object.assign(b, a) // == bPerforms left-to-right function composition.
Use Array.reduce() with the spread operator (...) to perform left-to-right function composition.
The first (leftmost) function can accept one or more arguments; the remaining functions must be unary.
const pipeFunctions = (...fns) => fns.reduce((f, g) => (...args) => g(f(...args)));const add5 = x => x + 5
const multiply = (x, y) => x * y
const multiplyAndAdd5 = pipeFunctions(multiply, add5)
multiplyAndAdd5(5, 2) // 15Converts an asynchronous function to return a promise.
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 2sTakes a variadic function and returns a closure that accepts an array of arguments to map to the inputs of the function.
Use closures and the spread operator (...) to map the array of arguments to the inputs of the function.
const spreadOver = fn => argsArr => fn(...argsArr);const arrayMax = spreadOver(Math.max)
arrayMax([1,2,3]) // 3
arrayMax([1,2,4]) // 4计算数组中数字的最大公约数。
使用 Array.reduce() 和 gcd 递归计算数组中的最大公约数。
const arrayGcd = arr =>{
const gcd = (x, y) => !y ? x : gcd(y, x % y);
return arr.reduce((a,b) => gcd(a,b));
}
// arrayGcd([1,2,3,4,5]) -> 1
// arrayGcd([4,8,12]) -> 4其中
const gcd = (x, y) => !y ? x : gcd(y, x % y);
定义的是一个使用辗转相除法递归计算两数最大公约数的函数
当y为0时，x就是最大公约数，否则进一步对y和x与y取模运算的结果使用辗转相除法，直到y为0
计算数组中数字的最小公倍数。
使用 Array.reduce() 和 lcm 递归计算最小公倍数。
const arrayLcm = arr =>{
const gcd = (x, y) => !y ? x : gcd(y, x % y);
const lcm = (x, y) => (x*y)/gcd(x, y);
return arr.reduce((a,b) => lcm(a,b));
}
// arrayLcm([1,2,3,4,5]) -> 60
// arrayLcm([4,8,12]) -> 24其中
const lcm = (x, y) => (x*y)/gcd(x, y);
定义的是最小公倍数计算的公式，两数之积处以两数的最大公约数就得到两数的最小公倍数
返回数组中的最大值
使用 Math.max() 结合扩展运算符 (...) 得到数组中的最大值。
const arrayMax = arr => Math.max(...arr);
// arrayMax([10, 1, 5]) -> 10返回数组中的最小值。
使用 Math.min() 结合扩展运算符 (...) 得到数组中的最小值。
const arrayMin = arr => Math.min(...arr);arrayMin([10, 1, 5]) // 1将一个数组分成特定长度的若干数组。
使用Array.from()创建新的数组。
使用Array.slice()将新数组的每个元素映射到size长度的区块。
如果原始数组不能均匀拆分, 则最终的块将包含剩余的元素。
const chunk = (arr, size) =>
Array.from({length: Math.ceil(arr.length / size)}, (v, i) => arr.slice(i * size, i * size + size));
chunk([1,2,3,4,5], 2) // [[1,2],[3,4],[5]]Array.from()的目的是产生一个数组
第一个参数是一个对象，length就是这个新数组的length
第二个参数是一个函数，新数组中的每个元素会执行该函数，这里定义的函数返回的是一个数组，它是根据原数组（arr）和分块大小（size）之间特定的关系而得到的，也就是新数组当前索引位置（i）处的chunk
移除数组中表示否的元素。
使用 Array.filter() 过滤掉否值 (false, null, 0, "", undefined, and NaN).
const compact = arr => arr.filter(Boolean);compact([0, 1, false, 2, '', 3, 'a', 'e'*23, NaN, 's', 34]) // [ 1, 2, 3, 'a', 's', 34 ]统计数组中某个值出现的次数。
使用 Array.reduce() ，每次遇到特定的值就使计数器加1。
const countOccurrences = (arr, value) => arr.reduce((a, v) => v === value ? a + 1 : a + 0, 0);countOccurrences([1,1,2,1,2,3], 1) // 3深度扁平化一个数组。
使用递归。
使用 Array.concat() 结合一个空数组 ([]) 和扩展运算符 (...) 扁平化一个数组。
对数组中的每个元素递归扁平。
const deepFlatten = arr => [].concat(...arr.map(v => Array.isArray(v) ? deepFlatten(v) : v));deepFlatten([1,[2],[[3],4],5]) // [1,2,3,4,5]返回两个数组中的不同元素。
使用 b初始化一个Set , 然后用 Array.filter() 过滤掉 a 中有而 b中没有的值。
const difference = (a, b) => { const s = new Set(b); return a.filter(x => !s.has(x)); };difference([1,2,3], [1,2,4]) // [3]set是ES6中新扩展的数据结构
set类似于数组，但是set中不能有重复的元素
一个数组去重的新方法：Array.from(new Set(array))
过滤掉数组中比较函数（或者说算子）不返回 true的值。
使用 Array.filter() 和 Array.find() 找到适当的值。
const differenceWith = (arr, val, comp) => arr.filter(a => !val.find(b => comp(a, b)));differenceWith([1, 1.2, 1.5, 3], [1.9, 3], (a,b) => Math.round(a) == Math.round(b)) // [1, 1.2]返回数组中不重复的值。（其实就是数组去重）
使用 ES6的 Set 和 ...rest 操作符来去除重复的值。
const distinctValuesOfArray = arr => [...new Set(arr)];distinctValuesOfArray([1,2,2,3,4,4,5]) // [1,2,3,4,5]移除数组中的元素，直到函数返回的结果是 true。最后返回包含剩余元素的数组。
循环整个数组，使用 Array.slice() 删除当前数组的第一个元素，直到一个元素返回 true。
const dropElements = (arr, func) => {
while (arr.length > 0 && !func(arr[0])) arr = arr.slice(1);
return arr;
};dropElements([1, 2, 3, 4], n => n >= 3) // [3,4]乍一看还以为是实现了一个filter
实际上实际上效果是从头遍历一个数组，只要有一个满足条件就停止循环，返回剩余数组
dropElements([1, 2, 3, 4, 1, 2], n => n >= 3) // [3,4,1,2]
返回一个移除了右边 n 个元素的新数组
使用 Array.slice()
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) // []返回一个数组中每 nth 个元素。
使用 Array.filter()
const everyNth = (arr, nth) => arr.filter((e, i) => i % nth === nth - 1);everyNth([1,2,3,4,5,6], 2) // [ 2, 4, 6 ]过滤出数组中不重复的元素。
使用 Array.filter()
const filterNonUnique = arr => arr.filter(i => arr.indexOf(i) === arr.lastIndexOf(i));filterNonUnique([1,2,2,3,4,4,5]) // [1,3,5]indexOf是返回第一个匹配的索引位置，lastIndexOf是返回最后一个匹配的索引位置
两者不相等说明数组中存在至少一个与之相同的元素
扁平化一个数组。
const flatten = arr => [ ].concat(...arr);flatten([1,[2],3,4]) // [1,2,3,4]这段代码只能对二维数组有效
如果是更复杂的多维数组，应该使用前面提到的deepFlatten
将一个数组展开（扁平化）到一定深度。
使用递归，逐层降低深度
使用 Array.reduce() 和 Array.concat() 把元素或子数组融合到一起
当深度 depth 等于 1 时停止递归
当第二个参数省略的时候, 默认只降低 1 层深度depth 。
const flattenDepth = (arr, depth = 1) =>
depth != 1 ? arr.reduce((a, v) => a.concat(Array.isArray(v) ? flattenDepth(v, depth - 1) : v), [])
: arr.reduce((a, v) => a.concat(v), []);flattenDepth([1,[2],3,4]) // [1,2,3,4]Groups the elements of an array based on the given function.
Use Array.map() to map the values of an array to a function or property name.
Use Array.reduce() to create an object, where the keys are produced from the mapped results.
const groupBy = (arr, func) =>
arr.map(typeof func === 'function' ? func : val => val[func])
.reduce((acc, val, i) => { acc[val] = (acc[val] || []).concat(arr[i]); return acc; }, {});groupBy([6.1, 4.2, 6.3], Math.floor) // {4: [4.2], 6: [6.1, 6.3]}
groupBy(['one', 'two', 'three'], 'length') // {3: ['one', 'two'], 5: ['three']}map之后得到了一个新的数组，这个数组是原数组中元素func作用后的值
比如这两个例子中map之后的数组是[6,4,6]和[3,3,5]
然后再和原数组结合生成一个以当前数组为健原数组为值的对象
如果原数组对应的健已被记录，就用concat连接
Returns the head of a list.
Use arr[0] to return the first element of the passed array.
const head = arr => arr[0];head([1,2,3]) // 1emmmmmm...
不写了吧
Returns all the elements of an array except the last one.
Use arr.slice(0,-1) to return all but the last element of the array.
const initial = arr => arr.slice(0, -1);initial([1,2,3]) // [1,2]也可以用 arr.pop();return arr 实现
�初始化一个指定行列数以及值的二维数组。
使用 Array.map() 生成 h 行每行长度为w的新数组，同时初始化数组内元素的值。
如果没有给定元素值，则默认为 null。
const initialize2DArray = (w, h, val = null) => Array(h).fill().map(() => Array(w).fill(val));initialize2DArray(2, 2, 0) // [[0,0], [0,0]]初始化一个数组，包含从 start 到 end 这段数字。
使用 Array((end + 1) - start) 创建一个拥有目标长度的数组, Array.map() 来填充一段数字
省略 start 则默认为 0.
const initializeArrayWithRange = (end, start = 0) =>
Array.from({ length: (end + 1) - start }).map((v, i) => i + start);initializeArrayWithRange(5) // [0,1,2,3,4,5]
initializeArrayWithRange(7, 3) // [3,4,5,6,7]Array(x)和Array.from({length:x})的区别：
Array(x)会生成长度为x的空数组，这个空数组如果访问的话会是[empty item]，map对这中空元素似乎无法操作
Array.from({length:x})也会生成长度为x的空数组，不同的是，访问这个数组的时候可以看到数组内每个元素都是undefined，map当然可以对这类数据进行操作
所以如果想用Array来实现相同效果的话，可以用Array((end + 1) - start).fill(x).map((v, i) => i + start)
Initializes and fills an array with the specified 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 initializeArrayWithValues = (n, value = 0) => Array(n).fill(value);initializeArrayWithValues(5, 2) // [2,2,2,2,2]Returns a list of elements that exist in both arrays.
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]Returns the last element in an array.
Use arr.length - 1 to compute the index of the last element of the given array and returning it.
const last = arr => arr[arr.length - 1];last([1,2,3]) // 3Maps the values of an array to an object using a function, where the key-value pairs consist of the original value as the key and the mapped value.
Use an anonymous inner function scope to declare an undefined memory space, using closures to store a return value. Use a new Array to store the array with a map of the function over its data set and a comma operator to return a second step, without needing to move from one context to another (due to closures and order of operations).
const mapObject = (arr, fn) =>
(a => (a = [arr, arr.map(fn)], a[0].reduce((acc, val, ind) => (acc[val] = a[1][ind], acc), {})))();const squareIt = arr => mapObject(arr, a => a*a)
squareIt([1,2,3]) // { 1: 1, 2: 4, 3: 9 }Returns the nth element of an array.
Use Array.slice() to get an array containing the nth element at the first place.
If the index is out of bounds, return [].
Omit the second argument, n, to get the first element of the array.
const nthElement = (arr, n = 0) => (n > 0 ? arr.slice(n, n + 1) : arr.slice(n))[0];nthElement(['a','b','c'],1) // 'b'
nthElement(['a','b','b'],-3) // 'a'Picks the key-value pairs corresponding to the given keys from an object.
Use Array.reduce() to convert the filtered/picked keys back to an object with the corresponding key-value pair if the key exists 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 }Mutates the original array to filter out the values specified.
Use Array.filter() and Array.includes() to pull out the values that are not needed.
Use Array.length = 0 to mutate the passed in an array by resetting it's length to zero and Array.push() to re-populate it with only the pulled values.
(For a snippet that does not mutate the original array see without)
const pull = (arr, ...args) => {
let argState = Array.isArray(args[0]) ? args[0] : args;
let pulled = arr.filter((v, i) => !argState.includes(v));
arr.length = 0;
pulled.forEach(v => arr.push(v));
};let myArray1 = ['a', 'b', 'c', 'a', 'b', 'c'];
pull(myArray1, 'a', 'c');
console.log(myArray1) // [ 'b', 'b' ]
let myArray2 = ['a', 'b', 'c', 'a', 'b', 'c'];
pull(myArray2, ['a', 'c']);
console.log(myArray2) // [ 'b', 'b' ]Mutates the original array to filter out the values at the specified indexes.
Use Array.filter() and Array.includes() to pull out the values that are not needed.
Use Array.length = 0 to mutate the passed in an array by resetting it's length to zero and Array.push() to re-populate it with only the pulled values.
Use Array.push() to keep track of pulled values
const pullAtIndex = (arr, pullArr) => {
let removed = [];
let pulled = arr.map((v, i) => pullArr.includes(i) ? removed.push(v) : v)
.filter((v, i) => !pullArr.includes(i));
arr.length = 0;
pulled.forEach(v => arr.push(v));
return removed;
};let myArray = ['a', 'b', 'c', 'd'];
let pulled = pullAtIndex(myArray, [1, 3]);
console.log(myArray); // [ 'a', 'c' ]
console.log(pulled); // [ 'b', 'd' ]Mutates the original array to filter out the values specified. Returns the removed elements.
Use Array.filter() and Array.includes() to pull out the values that are not needed.
Use Array.length = 0 to mutate the passed in an array by resetting it's length to zero and Array.push() to re-populate it with only the pulled values.
Use Array.push() to keep track of pulled values
const pullAtValue = (arr, pullArr) => {
let removed = [],
pushToRemove = arr.forEach((v, i) => pullArr.includes(v) ? removed.push(v) : v),
mutateTo = arr.filter((v, i) => !pullArr.includes(v));
arr.length = 0;
mutateTo.forEach(v => arr.push(v));
return removed;
};let myArray = ['a', 'b', 'c', 'd'];
let pulled = pullAtValue(myArray, ['b', 'd']);
console.log(myArray); // [ 'a', 'c' ]
console.log(pulled); // [ 'b', 'd' ]Removes elements from an array for which the given function returns false.
Use Array.filter() to find array elements that return truthy values and Array.reduce() to remove elements using Array.splice().
The func is invoked with three arguments (value, index, array).
const remove = (arr, func) =>
Array.isArray(arr) ? arr.filter(func).reduce((acc, val) => {
arr.splice(arr.indexOf(val), 1); return acc.concat(val);
}, [])
: [];remove([1, 2, 3, 4], n => n % 2 == 0) // [2, 4]Returns a random element from an array.
Use Math.random() to generate a random number, multiply it by length and round it of to the nearest whole number using Math.floor().
This method also works with strings.
const sample = arr => arr[Math.floor(Math.random() * arr.length)];sample([3, 7, 9, 11]) // 9Randomizes the order of the values of an array, returning a new array.
Uses the Fisher-Yates algoritm to reorder the elements of the array, based on the Lodash implementation, but as a pure function.
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]
console.log(foo) // [1,2,3]Returns an array of elements that appear in both 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]Returns the symmetric difference between two arrays.
Create a Set from each array, then use Array.filter() on each of them to only keep values not contained in the other.
const symmetricDifference = (a, b) => {
const sA = new Set(a), sB = new Set(b);
return [...a.filter(x => !sB.has(x)), ...b.filter(x => !sA.has(x))];
};symmetricDifference([1,2,3], [1,2,4]) // [3,4]Returns all elements in an array except for the first one.
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]Returns an array with n elements removed from the beginning.
Use Array.slice() to create a slice of the array with n elements taken 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) // []Returns an array with n elements removed from the end.
Use Array.slice() to create a slice of the array with n elements taken 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]Returns every element that exists in any of the two arrays once.
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]Filters out the elements of an array, that have one of the specified values.
Use Array.filter() to create an array excluding(using !Array.includes()) all given values.
(For a snippet that mutates the original array see pull)
const without = (arr, ...args) => arr.filter(v => !args.includes(v));without([2, 1, 2, 3], 1, 2) // [3]Creates an array of elements, grouped based on the position in the original arrays.
Use Math.max.apply() to get the longest array in the arguments.
Creates an array with that length as return value and use Array.from() with a map-function to create an array of grouped elements.
If lengths of the argument-arrays vary, undefined is used where no value could be found.
const zip = (...arrays) => {
const maxLength = Math.max(...arrays.map(x => x.length));
return Array.from({length: maxLength}).map((_, i) => {
return Array.from({length: arrays.length}, (_, k) => arrays[k][i]);
});
};zip(['a', 'b'], [1, 2], [true, false]); // [['a', 1, true], ['b', 2, false]]
zip(['a'], [1, 2], [true, false]); // [['a', 1, true], [undefined, 2, false]]Given an array of valid property identifiers and an array of values, return an object associating the properties to the values.
Since an object can have undefined values but not undefined property pointers, the array of properties is used to decide the structure of the resulting object using Array.reduce().
const zipObject = (props, values) => props.reduce((obj, prop, index) => (obj[prop] = values[index], obj), {});zipObject(['a','b','c'], [1,2]) // {a: 1, b: 2, c: undefined}
zipObject(['a','b'], [1,2,3]) // {a: 1, b: 2}Converts the given array elements into <li> tags and appends them to the list of the given id.
Use Array.map() and document.querySelector() to create a list of html tags.
const arrayToHtmlList = (arr, listID) => arr.map(item => document.querySelector('#' + listID).innerHTML += `<li>${item}</li>`);arrayToHtmlList(['item 1', 'item 2'],'myListID')Returns true if the bottom of the page is visible, false otherwise.
Use 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() // trueReturns the current URL.
Use window.location.href to get current URL.
const currentURL = () => window.location.href;currentURL() // 'https://google.com'Detects wether the website is being opened in a mobile device or a desktop/laptop.
Use a regular expression to test the navigator.userAgent property to figure out if the device is a mobile device or a desktop/laptop.
const detectDeviceType = () => /Android|webOS|iPhone|iPad|iPod|BlackBerry|IEMobile|Opera Mini/i.test(navigator.userAgent) ? 'Mobile' : 'Desktop';detectDeviceType() // "Mobile"
detectDeviceType() // "Desktop"Returns true if the element specified is visible in the viewport, false otherwise.
Use Element.getBoundingClientRect() and the window.inner(Width|Height) values
to determine if a given element is visible in the viewport.
Omit the second argument to determine if the element is entirely visible, or specify true to determine if
it is partially visible.
const elementIsVisibleInViewport = (el, partiallyVisible = false) => {
const { top, left, bottom, right } = el.getBoundingClientRect();
const { innerHeight, innerWidth } = window;
return partiallyVisible
? ((top > 0 && top < innerHeight) || (bottom > 0 && bottom < innerHeight)) &&
((left > 0 && left < innerWidth) || (right > 0 && right < innerWidth))
: top >= 0 && left >= 0 && bottom <= innerHeight && right <= innerWidth;
};// e.g. 100x100 viewport and a 10x10px element at position {top: -1, left: 0, bottom: 9, right: 10}
elementIsVisibleInViewport(el) // false // (not fully visible)
elementIsVisibleInViewport(el, true) // true // (partially visible)Returns the scroll position of the current page.
Use pageXOffset and pageYOffset if they are defined, otherwise scrollLeft and scrollTop.
You can omit el to use a default value of window.
const getScrollPosition = (el = window) =>
({x: (el.pageXOffset !== undefined) ? el.pageXOffset : el.scrollLeft,
y: (el.pageYOffset !== undefined) ? el.pageYOffset : el.scrollTop});getScrollPosition() // {x: 0, y: 200}Returns an object containing the parameters of the current URL.
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'}Redirects the page to HTTPS if its currently in HTTP. Also, pressing the back button doesn't take it back to the HTTP page as its replaced in the history.
Use location.protocol to get the protocol currently being used. If it's not HTTPS, use location.replace() to replace the existing page with the HTTPS version of the page. Use location.href to get the full address, split it with String.split() and remove the protocol part of the URL.
const httpsRedirect = () => {
if (location.protocol !== 'https:') location.replace('https://' + location.href.split('//')[1]);
};Redirects to a specified 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')Smooth-scrolls to the top of the page.
Get distance from top using document.documentElement.scrollTop or document.body.scrollTop.
Scroll by a fraction of the distance from the 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()Returns the difference (in days) between two dates.
Calculate the difference (in days) between two Date objects.
const getDaysDiffBetweenDates = (dateInitial, dateFinal) => (dateFinal - dateInitial) / (1000 * 3600 * 24);getDaysDiffBetweenDates(new Date("2017-12-13"), new Date("2017-12-22")) // 9Converts a JSON object to a date.
Use Date(), to convert dates in JSON format to readable format (dd/mm/yyyy).
const JSONToDate = arr => {
const dt = new Date(parseInt(arr.toString().substr(6)));
return `${dt.getDate()}/${dt.getMonth() + 1}/${dt.getFullYear()}`;
};JSONToDate(/Date(1489525200000)/) // "14/3/2017"Converts a date from American format to English format.
Use Date.toISOString(), split('T') and replace() to convert a date from American format to the English format.
Throws an error if the passed time cannot be converted to a date.
const toEnglishDate = (time) => { try { return new Date(time).toISOString().split('T')[0].replace(/-/g, '/'); } catch (e) {} };toEnglishDate('09/21/2010') // '21/09/2010'Results in a string representation of tomorrow's date.
Use new Date() to get today's date, adding 86400000 of seconds to it(24 hours), using toISOString to convert Date object to string.
const tomorrow = () => new Date(new Date().getTime() + 86400000).toISOString().split('T')[0];tomorrow() // 2017-12-27 (if current date is 2017-12-26)Chains asynchronous functions.
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'); }
])Performs right-to-left function composition.
Use Array.reduce() to perform right-to-left function composition.
The last (rightmost) function can accept one or more arguments; the remaining functions must be unary.
const compose = (...fns) => fns.reduce((f, g) => (...args) => f(g(...args)));const add5 = x => x + 5
const multiply = (x, y) => x * y
const multiplyAndAdd5 = compose(add5, multiply)
multiplyAndAdd5(5, 2) // 15Curries a function.
Use recursion.
If the number of provided arguments (args) is sufficient, call the passed function fn.
Otherwise, return a curried function fn 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 = (fn, arity = fn.length, ...args) =>
arity <= args.length
? fn(...args)
: curry.bind(null, fn, arity, ...args);curry(Math.pow)(2)(10) // 1024
curry(Math.min, 3)(10)(50)(2) // 2Logs the name of a function.
Use console.debug() and the name property of the passed method to log the method's name to the debug channel of the console.
const functionName = fn => (console.debug(fn.name), fn);functionName(Math.max) // max (logged in debug channel of console)Runs an array of promises in series.
Use Array.reduce() to create a promise chain, where each promise returns the next promise when resolved.
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 completeDelays the execution of an asynchronous function.
Delay executing part of an async function, by putting it to sleep, returning a Promise.
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.');
}Negates a predicate function.
Take a predicate function and apply not to it with its arguments.
const negate = func => (...args) => !func(...args);filter([1, 2, 3, 4, 5, 6], negate(isEven)) // [1, 3, 5]
negate(isOdd)(1) // falseReturns the average of an array of numbers.
Use Array.reduce() to add each value to an accumulator, initialized with a value of 0, divide by the length of the array.
const arrayAverage = arr => arr.reduce((acc, val) => acc + val, 0) / arr.length;arrayAverage([1,2,3]) // 2Returns the sum of an array of numbers.
Use Array.reduce() to add each value to an accumulator, initialized with a value of 0.
const arraySum = arr => arr.reduce((acc, val) => acc + val, 0);arraySum([1,2,3,4]) // 10Clamps num within the inclusive range specified by the boundary values a and b.
If num falls within the range, return num.
Otherwise, return the nearest number in the range.
const clampNumber = (num, a, b) => Math.max(Math.min(num, Math.max(a, b)), Math.min(a, b));clampNumber(2, 3, 5) // 3
clampNumber(1, -1, -5) // -1
clampNumber(3, 2, 4) // 3Applies the Collatz algorithm.
If n is even, return n/2. Otherwise, return 3n+1.
const collatz = n => (n % 2 == 0) ? (n / 2) : (3 * n + 1);collatz(8) // 4
collatz(5) // 16Converts a number to an array of digits.
Convert the number to a string, using spread operators in ES6([...string]) build an array.
Use Array.map() and parseInt() to transform each value to an integer.
const digitize = n => [...'' + n].map(i => parseInt(i));digitize(123) // [1, 2, 3]Returns the 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) // 2.23606797749979Calculates the factorial of a number.
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.
Throws an exception if n is a negative number.
const factorial = n =>
n < 0 ? (() => { throw new TypeError('Negative numbers are not allowed!'); })()
: n <= 1 ? 1 : n * factorial(n - 1);factorial(6) // 720Generates an array, containing the Fibonacci sequence, up until the nth term.
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.from({ length: n}).reduce((acc, val, i) => acc.concat(i > 1 ? acc[i - 1] + acc[i - 2] : i), []);fibonacci(6) // 720Returns the number of fibonnacci numbers up to num(0 and num inclusive).
Use a mathematical formula to calculate the number of fibonacci numbers until num.
const fibonacciCountUntilNum = num =>
Math.ceil(Math.log(num * Math.sqrt(5) + 1 / 2) / Math.log((Math.sqrt(5) + 1) / 2));fibonacciCountUntilNum(10) // 7Generates an array, containing the Fibonacci sequence, up until the nth term.
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.
Uses a mathematical formula to calculate the length of the array required.
const fibonacciUntilNum = num => {
let n = Math.ceil(Math.log(num * Math.sqrt(5) + 1 / 2) / Math.log((Math.sqrt(5) + 1) / 2));
return Array.from({ length: n}).reduce((acc, val, i) => acc.concat(i > 1 ? acc[i - 1] + acc[i - 2] : i), []);
};fibonacciCountUntilNum(10) // 7Calculates the greatest common divisor between two numbers.
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) // 4Calculates the Hamming distance between two values.
Use XOR operator (^) to find the bit difference between the two numbers, convert to a 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) // 1Checks if the given number falls within the given range.
Use arithmetic comparison to check if the given number is in the specified range.
If the second parameter, end, is not specified, the range is considered to be from 0 to start.
const inRange = (n, start, end = null) => {
if (end && start > end) end = [start, start = end][0];
return (end == null) ? (n >= 0 && n < start) : (n >= start && n < end);
};inRange(3, 2, 5) // true
inRange(3, 4) // true
inRange(2, 3, 5) // false
inrange(3, 2) // falseChecks if the given number is an Armstrong number or not.
Convert the given number into an array of digits. Use Math.pow() to get the appropriate power for each digit and sum them up. If the sum is equal to the number itself, return true otherwise false.
const isArmstrongNumber = digits =>
(arr => arr.reduce((a, d) => a + Math.pow(parseInt(d), arr.length), 0) == digits)((digits + '').split(''));isArmstrongNumber(1634) // true
isArmstrongNumber(371) // true
isArmstrongNumber(56) // falseChecks if the first numeric argument is divisible by the second one.
Use the modulo operator (%) to check if the remainder is equal to 0.
const isDivisible = (dividend, divisor) => dividend % divisor === 0;isDivisible(6,3) // trueReturns true if the given number is even, false otherwise.
Checks whether a number is odd or even using the modulo (%) operator.
Returns true if the number is even, false if the number is odd.
const isEven = num => num % 2 === 0;isEven(3) // falseChecks if the provided integer is a prime number.
Check numbers from 2 to the square root of the given number.
Return false if any of them divides the given number, else return true, unless the number is less than 2.
const isPrime = num => {
const boundary = Math.floor(Math.sqrt(num));
for (var i = 2; i * i <= boundary; i++) if (num % i == 0) return false;
return num >= 2;
};isPrime(11) // true
isPrime(12) // falseReturns the least common multiple of two numbers.
Use the greatest common divisor (GCD) formula and Math.abs() to determine the least common multiple.
The GCD formula uses recursion.
const lcm = (x, y) => {
const gcd = (x, y) => !y ? x : gcd(y, x % y);
return Math.abs(x * y) / (gcd(x, y));
};lcm(12,7) // 84Returns the median of an array of numbers.
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]) // 3.5Returns true if the given string is a palindrome, false otherwise.
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') // trueUses the percentile formula to calculate how many numbers in the given array are less or equal to the given value.
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) // 55Returns the powerset of a given array of numbers.
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]]Generates primes up to a given number, using the Sieve of Eratosthenes.
Generate an array from 2 to the given number. Use Array.filter() to filter out the values divisible by any number from 2 to the square root of the provided number.
const primes = num => {
let arr = Array.from({length: num - 1}).map((x, i) => i + 2),
sqroot = Math.floor(Math.sqrt(num)),
numsTillSqroot = Array.from({length: sqroot - 1}).map((x, i) => i + 2);
numsTillSqroot.forEach(x => arr = arr.filter(y => ((y % x) !== 0) || (y == x)));
return arr;
};primes(10) // [2,3,5,7]Returns a random integer in the specified 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) // 2Returns a random number in the specified range.
Use Math.random() to generate a random value, map it to the desired range using multiplication.
const randomNumberInRange = (min, max) => Math.random() * (max - min) + min;randomNumberInRange(2,10) // 6.0211363285087005Rounds a number to a specified amount of digits.
Use Math.round() and template literals to round the number to the specified number of digits.
Omit the second argument, decimals to round to an integer.
const round = (n, decimals = 0) => Number(`${Math.round(`${n}e${decimals}`)}e-${decimals}`);round(1.005, 2) // 1.01Returns the standard deviation of an array of numbers.
Use Array.reduce() to calculate the mean, variance and the sum of the variance of the values, the variance of the values, then
determine the standard deviation.
You can omit the second argument to get the sample standard deviation or set it to true to get the population standard deviation.
const standardDeviation = (arr, usePopulation = false) => {
const mean = arr.reduce((acc, val) => acc + val, 0) / arr.length;
return Math.sqrt(
arr.reduce((acc, val) => acc.concat(Math.pow(val - mean, 2)), [])
.reduce((acc, val) => acc + val, 0) / (arr.length - (usePopulation ? 0 : 1))
);
};standardDeviation([10,2,38,23,38,23,21]) // 13.284434142114991 (sample)
standardDeviation([10,2,38,23,38,23,21], true) // 12.29899614287479 (population)Performs speech synthesis (experimental).
Use SpeechSynthesisUtterance.voice and window.speechSynthesis.getVoices() to convert a message to speech.
Use window.speechSynthesis.speak() to play the message.
Learn more about the SpeechSynthesisUtterance interface of the Web Speech API.
const speechSynthesis = message => {
const msg = new SpeechSynthesisUtterance(message);
msg.voice = window.speechSynthesis.getVoices()[0];
window.speechSynthesis.speak(msg);
};speechSynthesis('Hello, World') // // plays the messageWrites a JSON object to a file.
Use fs.writeFile(), template literals and JSON.stringify() to write a json object to a .json file.
const fs = require('fs');
const JSONToFile = (obj, filename) => fs.writeFile(`${filename}.json`, JSON.stringify(obj, null, 2));JSONToFile({test: "is passed"}, 'testJsonFile') // writes the object to 'testJsonFile.json'Returns an array of lines from the specified file.
Use readFileSync function in fs node package to create a Buffer from a file.
convert buffer to string using toString(encoding) function.
creating an array from contents of file by spliting file content line by line (each \n).
const fs = require('fs');
const readFileLines = filename => fs.readFileSync(filename).toString('UTF8').split('\n');/*
contents of test.txt :
line1
line2
line3
___________________________
*/
let arr = readFileLines('test.txt')
console.log(arr) // ['line1', 'line2', 'line3']Removes any properties except the ones specified from a JSON object.
Use Object.keys() method to loop over given JSON object and deleting keys that are not included in given array.
Also if you give it a special key (childIndicator) it will search deeply inside it to apply function to inner objects too.
const cleanObj = (obj, keysToKeep = [], childIndicator) => {
Object.keys(obj).forEach(key => {
if (key === childIndicator) {
cleanObj(obj[key], keysToKeep, childIndicator);
} else if (!keysToKeep.includes(key)) {
delete obj[key];
}
});
return obj;
};const testObj = {a: 1, b: 2, children: {a: 1, b: 2}}
cleanObj(testObj, ["a"],"children") // { a: 1, children : { a: 1}}Creates an object from the given 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}Creates an array of key-value pair arrays from an object.
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]])Returns a sorted array of objects ordered by properties and orders.
Uses a custom implementation of sort, that reduces the props array argument with a default value of 0, it uses destructuring to swap the properties position depending on the order passed. If no orders array is passed it sort by 'asc' by default.
const orderBy = (arr, props, orders) =>
arr.sort((a, b) =>
props.reduce((acc, prop, i) => {
if (acc === 0) {
const [p1, p2] = orders && orders[i] === 'desc' ? [b[prop], a[prop]] : [a[prop], b[prop]];
acc = p1 > p2 ? 1 : p1 < p2 ? -1 : 0;
}
return acc;
}, 0)
);const users = [{ 'name': 'fred', 'age': 48 },{ 'name': 'barney', 'age': 36 },
{ 'name': 'fred', 'age': 40 },{ 'name': 'barney', 'age': 34 }];
orderby(users, ['name', 'age'], ['asc', 'desc']) // [{name: 'barney', age: 36}, {name: 'barney', age: 34}, {name: 'fred', age: 48}, {name: 'fred', age: 40}]
orderby(users, ['name', 'age']) // [{name: 'barney', age: 34}, {name: 'barney', age: 36}, {name: 'fred', age: 40}, {name: 'fred', age: 48}]Retrieve a property that indicated by the selector from an object.
If the property does not exists returns undefined.
const select = (from, selector) =>
selector.split('.').reduce((prev, cur) => prev && prev[cur], from);const obj = {selector: {to: {val: 'val to select'}}};
select(obj, 'selector.to.val'); // 'val to select'Creates a shallow clone of an object.
Use Object.assign() and an empty object ({}) to create a shallow clone of the original.
const shallowClone = obj => Object.assign({}, obj);const a = { x: true, y: 1 };
const b = shallowClone(a);
a === b // falseChecks if the predicate (second argument) is truthy on all elements of a collection (first argument).
Use Array.every() to check if each passed object has the specified property and if it returns a truthy value.
const truthCheckCollection = (collection, pre) => (collection.every(obj => obj[pre]));truthCheckCollection([{"user": "Tinky-Winky", "sex": "male"}, {"user": "Dipsy", "sex": "male"}], "sex") // trueGenerates all anagrams of a string (contains duplicates).
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']Capitalizes the first letter of a string.
Use destructuring and toUpperCase() to capitalize first letter, ...rest to get array of characters after first letter and then Array.join('') to make it a string again.
Omit the lowerRest parameter to keep the rest of the string intact, or set it to true to convert to lowercase.
const capitalize = ([first, ...rest], lowerRest = false) =>
first.toUpperCase() + (lowerRest ? rest.join('').toLowerCase() : rest.join(''));capitalize('fooBar') // 'FooBar'
capitalize('fooBar', true) // 'Foobar'Capitalizes the first letter of every word in a string.
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!'Retuns number of vowels in provided string.
Use a regular expression to count the number of vowels (A, E, I, O, U) in a string.
const countVowels = str => (str.match(/[aeiou]/ig) || []).length;countVowels('foobar') // 3
countVowels('gym') // 0Escapes a string to use in a regular expression.
Use replace() to escape special characters.
const escapeRegExp = str => str.replace(/[.*+?^${}()|[\]\\]/g, '\\$&');escapeRegExp('(test)') // \\(test\\)Converts a string from camelcase.
Use replace() to remove underscores, hyphens, and spaces and convert words to camelcase.
Omit the second argument to use a default separator of _.
const fromCamelCase = (str, separator = '_') =>
str.replace(/([a-z\d])([A-Z])/g, '$1' + separator + '$2')
.replace(/([A-Z]+)([A-Z][a-z\d]+)/g, '$1' + separator + '$2').toLowerCase();fromCamelCase('someDatabaseFieldName', ' ') // 'some database field name'
fromCamelCase('someLabelThatNeedsToBeCamelized', '-') // 'some-label-that-needs-to-be-camelized'
fromCamelCase('someJavascriptProperty', '_') // 'some_javascript_property'Repeats a string n times using String.repeat()
If no string is provided the default is "" and the default number of times is 2.
const repeatString = (str = '', num = 2) => {
return num >= 0 ? str.repeat(num) : str;
};repeatString("abc",3) // 'abcabcabc'
repeatString("abc") // 'abcabc'Reverses a string.
Use split('') 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.split('').reverse().join('');reverseString('foobar') // 'raboof'Alphabetically sorts the characters in a string.
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'Converts a string to camelcase.
Break the string into words and combine them capitalizing the first letter of each word. For more detailed explanation of this Regex, visit this Site.
const toCamelCase = str => {
let s = str && str.match(/[A-Z]{2,}(?=[A-Z][a-z]+[0-9]*|\b)|[A-Z]?[a-z]+[0-9]*|[A-Z]|[0-9]+/g)
.map(x => x.slice(0, 1).toUpperCase() + x.slice(1).toLowerCase())
.join('');
return s.slice(0, 1).toLowerCase() + s.slice(1);
};toCamelCase("some_database_field_name") // 'someDatabaseFieldName'
toCamelCase("Some label that needs to be camelized") // 'someLabelThatNeedsToBeCamelized'
toCamelCase("some-javascript-property") // 'someJavascriptProperty'
toCamelCase("some-mixed_string with spaces_underscores-and-hyphens") // 'someMixedStringWithSpacesUnderscoresAndHyphens'Converts a string to kebab case.
Break the string into words and combine them using - as a separator.
For more detailed explanation of this Regex, visit this Site.
const toKebabCase = str =>
str && str.match(/[A-Z]{2,}(?=[A-Z][a-z]+[0-9]*|\b)|[A-Z]?[a-z]+[0-9]*|[A-Z]|[0-9]+/g)
.map(x => x.toLowerCase())
.join('-');toKebabCase("camelCase") // 'camel-case'
toKebabCase("some text") // 'some-text'
toKebabCase("some-mixed_string With spaces_underscores-and-hyphens") // 'some-mixed-string-with-spaces-underscores-and-hyphens'
toKebabCase("AllThe-small Things") // "all-the-small-things"
toKebabCase('IAmListeningToFMWhileLoadingDifferentURLOnMyBrowserAndAlsoEditingSomeXMLAndHTML') // "i-am-listening-to-fm-while-loading-different-url-on-my-browser-and-also-editing-xml-and-html"Converts a string to snake case.
Break the string into words and combine them using _ as a separator.
For more detailed explanation of this Regex, visit this Site.
const toSnakeCase = str => {
str && str.match(/[A-Z]{2,}(?=[A-Z][a-z]+[0-9]*|\b)|[A-Z]?[a-z]+[0-9]*|[A-Z]|[0-9]+/g)
.map(x => x.toLowerCase())
.join('_');
};toSnakeCase("camelCase") // 'camel_case'
toSnakeCase("some text") // 'some_text'
toSnakeCase("some-javascript-property") // 'some_javascript_property'
toSnakeCase("some-mixed_string With spaces_underscores-and-hyphens") // 'some_mixed_string_with_spaces_underscores_and_hyphens'
toSnakeCase("AllThe-small Things") // "all_the_smal_things"
toSnakeCase('IAmListeningToFMWhileLoadingDifferentURLOnMyBrowserAndAlsoEditingSomeXMLAndHTML') // "i_am_listening_to_fm_while_loading_different_url_on_my_browser_and_also_editing_some_xml_and_html"Truncates a string up to a specified length.
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 truncateString = (str, num) =>
str.length > num ? str.slice(0, num > 3 ? num - 3 : num) + '...' : str;truncateString('boomerang', 7) // 'boom...'Converts a given string into an array of words.
Use String.split() with a supplied pattern (defaults to non-alpha as a regex) to convert to an array of strings. Use Array.filter() to remove any empty strings.
Omit the second argument to use the default regex.
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"]Returns the first non-null/undefined argument.
Use Array.find() to return the first non null/undefined argument.
const coalesce = (...args) => args.find(_ => ![undefined, null].includes(_));coalesce(null,undefined,"",NaN, "Waldo") // ""Returns a customized coalesce function that returns the first argument that returns true from the provided argument validation function.
Use Array.find() to return the first argument that returns true from the provided argument validation function.
const coalesceFactory = valid => (...args) => args.find(valid);const customCoalesce = coalesceFactory(_ => ![null, undefined, "", NaN].includes(_))
customCoalesce(undefined, null, NaN, "", "Waldo") // "Waldo"Extends a 3-digit color code to a 6-digit color code.
Use Array.map(), split() and Array.join() to join the mapped array for converting a 3-digit RGB notated hexadecimal color-code to the 6-digit form.
String.slice() is used to remove # from string start since it's added once.
const extendHex = shortHex =>
'#' + shortHex.slice(shortHex.startsWith('#') ? 1 : 0).split('').map(x => x + x).join('');extendHex('#03f') // '#0033ff'
extendHex('05a') // '#0055aa'Returns the native type of a value.
Returns lowercased 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"Converts a color code to a rgb() or rgba() string if alpha value is provided.
Use bitwise right-shift operator and mask bits with & (and) operator to convert a hexadecimal color code (with or without prefixed with #) to a string with the RGB values. If it's 3-digit color code, first convert to 6-digit version. If an alpha value is provided alongside 6-digit hex, give rgba() string in return.
const hexToRGB = hex => {
let alpha = false, h = hex.slice(hex.startsWith('#') ? 1 : 0);
if (h.length === 3) h = [...h].map(x => x + x).join('');
else if (h.length === 8) alpha = true;
h = parseInt(h, 16);
return 'rgb' + (alpha ? 'a' : '') + '(' +
(h >>> (alpha ? 24 : 16)) + ', ' +
((h & (alpha ? 0x00ff0000 : 0x00ff00)) >>> (alpha ? 16 : 8)) + ', ' +
((h & (alpha ? 0x0000ff00 : 0x0000ff)) >>> (alpha ? 8 : 0)) +
(alpha ? `, ${(h & 0x000000ff)}` : '') + ')';
};hexToRGB('#27ae60ff') // 'rgba(39, 174, 96, 255)'
hexToRGB('27ae60') // 'rgb(39, 174, 96)'
hexToRGB('#fff') // 'rgb(255, 255, 255)'Checks if the given argument is an array.
Use Array.isArray() to check if a value is classified as an array.
const isArray = val => !!val && Array.isArray(val);isArray(null) // false
isArray([1]) // trueChecks if the given argument is a native boolean element.
Use typeof to check if a value is classified as a boolean primitive.
const isBoolean = val => typeof val === 'boolean';isBoolean(null) // false
isBoolean(false) // trueChecks if the given argument is a function.
Use typeof to check if a value is classified as a function primitive.
const isFunction = val => val && typeof val === 'function';isFunction('x') // false
isFunction(x => x) // trueChecks if the given argument is a number.
Use typeof to check if a value is classified as a number primitive.
const isNumber = val => typeof val === 'number';isNumber('1') // false
isNumber(1) // trueChecks if the given argument is a string.
Use typeof to check if a value is classified as a string primitive.
const isString = val => typeof val === 'string';isString(10) // false
isString('10') // trueChecks if the given argument is a symbol.
Use typeof to check if a value is classified as a symbol primitive.
const isSymbol = val => typeof val === 'symbol';isSymbol('x') // false
isSymbol(Symbol('x')) // trueGenerates a random hexadecimal color code.
Use Math.random to generate a random 24-bit(6x4bits) hexadecimal number. Use bit shifting and then convert it to an hexadecimal String using toString(16).
const randomHexColorCode = () => {
let n = (Math.random() * 0xfffff | 0).toString(16);
return '#' + (n.length !== 6
? (Math.random() * 0xf | 0).toString(16) + n : n);
}; randomHexColorCode() // "#e34155"
randomHexColorCode() // "#fd73a6"
randomHexColorCode() // "#4144c6"Converts the values of RGB components to a color code.
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'This algorithm is a simple hash-algorithm that hashes it input string s into a whole number.
Use split('') and Array.reduce() to create a hash of the input string, utilizing bit shifting.
const sdbm = str => {
let arr = str.split('');
return arr.reduce((hashCode, currentVal) =>
hashCode = currentVal.charCodeAt(0) + (hashCode << 6) + (hashCode << 16) - hashCode
,0)
}console.log(sdbm("name")) // -3521204949
console.log(sdbm("age")) // 808122783Measures the time taken by a function to execute.
Use console.time() and console.timeEnd() to measure the difference between the start and end times to determine how long the callback took to execute.
const timeTaken = callback => {
console.time('timeTaken'); const r = callback();
console.timeEnd('timeTaken'); return r;
};timeTaken(() => Math.pow(2, 10)) // 1024
// (logged): timeTaken: 0.02099609375msUse toLocaleString() to convert a float-point arithmetic to the Decimal mark form. It makes a comma separated string from a number.
const toDecimalMark = num => num.toLocaleString('en-US');toDecimalMark(12305030388.9087) // "12,305,030,388.9087"Adds an ordinal suffix to a number.
Use the modulo operator (%) to find values of single and tens digits.
Find which ordinal pattern digits match.
If digit is found in teens pattern, use teens ordinal.
const toOrdinalSuffix = num => {
const int = parseInt(num), digits = [(int % 10), (int % 100)],
ordinals = ['st', 'nd', 'rd', 'th'], oPattern = [1, 2, 3, 4],
tPattern = [11, 12, 13, 14, 15, 16, 17, 18, 19];
return oPattern.includes(digits[0]) && !tPattern.includes(digits[1]) ? int + ordinals[digits[0] - 1] : int + ordinals[3];
};toOrdinalSuffix("123") // "123rd"Generates a UUID.
Use crypto API to generate a UUID, compliant with RFC4122 version 4.
const UUIDGenerator = () =>
([1e7] + -1e3 + -4e3 + -8e3 + -1e11).replace(/[018]/g, c =>
(c ^ crypto.getRandomValues(new Uint8Array(1))[0] & 15 >> c / 4).toString(16)
);UUIDGenerator() // '7982fcfe-5721-4632-bede-6000885be57d'Returns true if the given value is a number, false otherwise.
Use !isNaN in combination with parseFloat() to check if the argument is a number.
Use isFinite() to check if the number is finite.
Use Number() to check if the coercion holds.
const validateNumber = n => !isNaN(parseFloat(n)) && isFinite(n) && Number(n) == n;validateNumber('10') // trueIcons made by Smashicons from www.flaticon.com is licensed by CC 3.0 BY.