img

花30秒或者更短的时间就能理解的Javascript代码段

  • 可以使用Ctrl + F 或者 command + F搜索
  • 代码段使用ES6编写,使用 Babel transpiler 保证兼容.
  • 作者在持续更新传送门

目录

Array

Browser

Date

Function

Math

Media

Node

Object

String

Utility

Array

arrayMax

返回数组中的最大值.

使用 Math.max() 配合展开操作符 (...) 得到数组中的最大值.

1
2
const arrayMax = arr => Math.max(...arr);
// arrayMax([10, 1, 5]) -> 10

⬆ back to top

arrayMin

返回数组中的最小值.

使用 Math.min() 配合展开操作符 (...) 得到数组中的最小值.

1
2
const arrayMin = arr => Math.min(...arr);
// arrayMin([10, 1, 5]) -> 1

⬆ back to top

chunk

将一个数组分割成几个数组段.

使用 Array.from() 创建一个适合它长度的新的数组
使用 Array.slice() 分割为指定 size 长度的数组段
如果指定的数组不能被平均分割,最后的块将包含剩余的元素。

1
2
3
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]]

⬆ back to top

compact

移除数组中的非真值

使用 Array.filter() 过滤非真值 (false, null, 0, "", undefined, 和 NaN).

1
2
const compact = (arr) => arr.filter(Boolean);
// compact([0, 1, false, 2, '', 3, 'a', 'e'*23, NaN, 's', 34]) -> [ 1, 2, 3, 'a', 's', 34 ]

⬆ back to top

countOccurrences

计算元素出现的次数.

使用 Array.reduce() 计算指定元素在数组中出现的次数

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

⬆ back to top

deepFlatten

深度降维

使用递归.
使用 Array.concat() 和一个空数组 ([]) 还有展开运算符 (...) 降维一个多维数组.

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

⬆ back to top

difference

返回两个数组的差集

创建一个 bSet, 然后使用 Array.filter() 查找 a 中不包含 b的元素.

1
2
const difference = (a, b) => { const s = new Set(b); return a.filter(x => !s.has(x)); };
// difference([1,2,3], [1,2,4]) -> [3]

⬆ back to top

distinctValuesOfArray

返回数组中不重复的元素

使用 ES6的 Set 和展开运算符 ...rest 过滤重复的元素.

1
2
const distinctValuesOfArray = arr => [...new Set(arr)];
// distinctValuesOfArray([1,2,2,3,4,4,5]) -> [1,2,3,4,5]

⬆ back to top

dropElements

给函数传递一个表达式和数组,只保留表达式为true的元素

1
2
3
4
5
const dropElements = (arr, func) => {
while (arr.length > 0 && !func(arr[0])) arr.shift();
return arr;
};
// dropElements([1, 2, 3, 4], n => n >= 3) -> [3,4]

⬆ back to top

everyNth

返回数组中每一个第n的元素.

使用 Array.filter() 返回每一个第n的元素.

1
2
const everyNth = (arr, nth) => arr.filter((e, i) => i % nth === 0);
// everyNth([1,2,3,4,5,6], 2) -> [ 1, 3, 5 ]

⬆ back to top

filterNonUnique

过滤不唯一的元素.

使用 Array.filter() 只保留唯一的元素.

1
2
const filterNonUnique = arr => arr.filter(i => arr.indexOf(i) === arr.lastIndexOf(i));
// filterNonUnique([1,2,2,3,4,4,5]) -> [1,3,5]

⬆ back to top

flatten

降维数组.

使用 Array.reduce() 获取到每一个元素然后使用 concat() 降维.

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

⬆ back to top

flattenDepth

根据指定的深度降维数组.

使用递归,为所有维度的数组降低一维.
使用 Array.reduce()Array.concat() 合并降维后的数组或元素.
此时如果 depth1 停止递归.

1
2
3
4
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],5]], 2) -> [1,2,[3],4,5]

⬆ back to top

groupBy

根据指定的表达式为数组分组

使用 Array.map() 映射为根据表达式或属性名值计算后的数组
使用 Array.reduce() 创建一个键值是上一步map出来的结果,值是相对应的数组的对象

1
2
3
4
5
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']}

⬆ back to top

返回集合的第一个元素

使用 arr[0] 返回给定数组的第一个元素.

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

⬆ back to top

initial

返回一个数组中除去最后一个元素的其他元素.

使用 arr.slice(0,-1) 返回除去最后一个元素的其他元素.

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

⬆ back to top

initializeArrayWithRange

初始化一个指定范围的数组

使用 Array(end-start) 创建一个期望长度的数组, 根据给定的范围使用Array.map()填充数组.
参数start 默认值为 0.

1
2
3
const initializeArrayWithRange = (end, start = 0) =>
Array.from({ length: end - start }).map((v, i) => i + start);
// initializeArrayWithRange(5) -> [0,1,2,3,4]

⬆ back to top

initializeArrayWithValues

初始化并且根据给定的值填充数组.

使用 Array(n) 创建一个期望长度的数组, 根据给定的值使用 fill(v) 填充数组.
参数 value 默认值为 0.

1
2
const initializeArrayWithValues = (n, value = 0) => Array(n).fill(value);
// initializeArrayWithValues(5, 2) -> [2,2,2,2,2]

⬆ back to top

intersection

返回两个数组的交集.

创建一个 bSet, 然后使用 aArray.filter() 查找含 b 元素.

1
2
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]

⬆ back to top

last

返回数组中的最后一个元素.

使用 arr.length - 1 计算出最后一个元素的索引,然后返回它的值.

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

⬆ back to top

mapObject

映射一个数组,结果是键值为他的每一个元素的值,值为给定表达式结果的对象

1
2
3
4
5
6
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 }
*/

⬆ back to top

nthElement

返回数组的第n个对象.

使用 Array.slice() 获取满足给定条件的数组的第一个元素
如果给定的索引超出范围,返回 [].
参数 n 默认为第一个元素

1
2
3
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'

⬆ back to top

pick

返回对象的一个拷贝,返回的对象只含有给定的键的键值对

1
2
3
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 }

⬆ back to top

pull

抽取数组中指定的元素

使用 Array.filter()Array.includes() 抽出不需要的元素.
使用 Array.length = 0 重置数组并且使用 Array.push() 重新填充抽取后的数组.

1
2
3
4
5
6
7
const pull = (arr, ...args) => {
let pulled = arr.filter((v, i) => !args.includes(v));
arr.length = 0; pulled.forEach(v => arr.push(v));
};
// let myArray = ['a', 'b', 'c', 'a', 'b', 'c'];
// pull(myArray, 'a', 'c');
// console.log(myArray) -> [ 'b', 'b' ]

⬆ back to top

remove

移除数组中给定表达式为 false. 的值

使用 Array.filter() 找到表达式为 true 的值,然后通过 Array.reduce() 使用 Array.splice() 移除.

1
2
3
4
5
6
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]

⬆ back to top

sample

返回数组的一个随机元素

使用 Math.random() 创建一个随机数,然后和 length 相乘之后通过 Math.floor() 找到一个最接近的数.

1
2
const sample = arr => arr[Math.floor(Math.random() * arr.length)];
// sample([3, 7, 9, 11]) -> 9

⬆ back to top

shuffle

打乱数组中值的顺序

使用 Array.sort() 重新排序, 使用 Math.random() - 0.5 作为compareFunction.

1
2
const shuffle = arr => arr.sort(() => Math.random() - 0.5);
// shuffle([1,2,3]) -> [2,3,1]

⬆ back to top

similarity

返回一个数组,它的值两个数组里面都存在.

使用 includes() 找出values不含有的元素,使用filter()移除.

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

⬆ back to top

symmetricDifference

返回两个数组的对称差异.

通过两个数组分别创建 Set, 然后使用 Array.filter() 找出不在另外一个集合中的元素.

1
2
3
4
5
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]

⬆ back to top

tail

返回数组中除去第一个元素的集合

如果数组length 大于 1, 返回 arr.slice(1) 否则就返回整个数组.

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

⬆ back to top

take

返回前n个元素.

1
2
3
const take = (arr, n = 1) => arr.slice(0, n);
// take([1, 2, 3], 5) -> [1, 2, 3]
// take([1, 2, 3], 0) -> []

⬆ back to top

takeRight

返回后n个元素.

1
2
3
const takeRight = (arr, n = 1) => arr.slice(arr.length - n, arr.length);
// takeRight([1, 2, 3], 2) -> [ 2, 3 ]
// takeRight([1, 2, 3]) -> [3]

⬆ back to top

union

合并两个集合(结果不含重复元素)

1
2
const union = (a, b) => Array.from(new Set([...a, ...b]));
// union([1,2,3], [4,3,2]) -> [1,2,3,4]

⬆ back to top

without

根据指定的值过滤数组

1
2
const without = (arr, ...args) => arr.filter(v => !args.includes(v));
// without([2, 1, 2, 3], 1, 2) -> [3]

⬆ back to top

zip

根据原始数组的位置把多个数组压缩

使用 Math.max.apply() 获取输入数组中最大的长度,根据这个长度使用Array.from()创建一个新的数组,之后把输入数组的映射压缩到里面,如果某个数组缺少元素使用undefined代替

1
2
3
4
5
6
7
8
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]]

⬆ back to top

Browser

bottomVisible

如果到达页面底部,返回true否则返回false

使用 scrollY, scrollHeightclientHeight 判断是否到达页面底部

1
2
3
const bottomVisible = () =>
document.documentElement.clientHeight + window.scrollY >= document.documentElement.scrollHeight || document.documentElement.clientHeight;
// bottomVisible() -> true

⬆ back to top

currentURL

返回当前页面的URL.

使用 window.location.href 获取当前页面URL.

1
2
const currentURL = () => window.location.href;
// currentUrl() -> 'https://google.com'

⬆ back to top

elementIsVisibleInViewport

如果一个元素在视口可见,返回true否则返回false

使用 Element.getBoundingClientRect()window.inner(Width|Height) 判断元素是否在视口可见,第二个参数设置为true表示是否部分可见,默认值为false

1
2
3
4
5
6
7
8
9
10
const elementIsVisibleInViewport = (el, partiallyVisible = false) => {
const { top, left, bottom, right } = el.getBoundingClientRect();
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)

⬆ back to top

getScrollPosition

返回滚动条在当前页面的位置.

如果 pageXOffsetpageYOffset 未定义,使用 scrollLeft and scrollTop.

1
2
3
4
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}

⬆ back to top

getURLParameters

返回URL查询字符串对象.

1
2
3
4
5
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'}

⬆ back to top

redirect

重定向到指定的URL.

1
2
3
const redirect = (url, asLink = true) =>
asLink ? window.location.href = url : window.location.replace(url);
// redirect('https://google.com')

⬆ back to top

scrollToTop

平滑滚动到页面顶部.

1
2
3
4
5
6
7
8
const scrollToTop = () => {
const c = document.documentElement.scrollTop || document.body.scrollTop;
if (c > 0) {
window.requestAnimationFrame(scrollToTop);
window.scrollTo(0, c - c / 8);
}
};
// scrollToTop()

⬆ back to top

Date

getDaysDiffBetweenDates

返回两个Date对象的天数差

1
2
const getDaysDiffBetweenDates = (dateInitial, dateFinal) => (dateFinal - dateInitial) / (1000 * 3600 * 24);
// getDaysDiffBetweenDates(new Date("2017-12-13"), new Date("2017-12-22")) -> 9

⬆ back to top

JSONToDate

转换一个JSON对象为时间.

1
2
3
4
5
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"

⬆ back to top

toEnglishDate

把美国时间转换为英国时间.

1
2
3
const toEnglishDate  = (time) =>
{try{return new Date(time).toISOString().split('T')[0].replace(/-/g, '/')}catch(e){return}};
// toEnglishDate('09/21/2010') -> '21/09/2010'

⬆ back to top

Function

chainAsync

串联异步方法.

1
2
3
4
5
6
7
8
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'); }
])
*/

⬆ back to top

compose

从右往左执行函数组合

1
2
3
4
5
6
7
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) -> 15
*/

⬆ back to top

curry

对函数进行柯里化

1
2
3
4
5
6
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) -> 2

⬆ back to top

functionName

打印函数名称

1
2
const functionName = fn => (console.debug(fn.name), fn);
// functionName(Math.max) -> max (logged in debug channel of console)

⬆ back to top

pipe

从左往右执行函数组合

1
2
3
4
5
6
7
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) -> 15
*/

⬆ back to top

promisify

把异步函数转化为promise

In Node 8+, you can use util.promisify

1
2
3
4
5
6
7
8
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 2s

⬆ back to top

runPromisesInSeries

执行一系列promise函数

1
2
3
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

⬆ back to top

sleep

延迟执行异步函数

Delay executing part of an async function, by putting it to sleep, returning a Promise.

1
2
3
4
5
6
7
8
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.');
}
*/

⬆ back to top

Math

arrayAverage

返回数组的平均值

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

⬆ back to top

arraySum

返回数组的和

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

⬆ back to top

collatz

实现Collatz算法.

如果 n 是偶数, 返回 n/2. 否则返回 3n+1.

1
2
3
const collatz = n => (n % 2 == 0) ? (n / 2) : (3 * n + 1);
// collatz(8) --> 4
// collatz(5) --> 16

⬆ back to top

digitize

把数字转为数组

1
2
const digitize = n => [...''+n].map(i => parseInt(i));
// digitize(2334) -> [2, 3, 3, 4]

⬆ back to top

distance

返回两点距离.

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

⬆ back to top

factorial

计算一个数字的阶乘.

1
2
3
4
const factorial = n =>
n < 0 ? (() => { throw new TypeError('Negative numbers are not allowed!') })()
: n <= 1 ? 1 : n * factorial(n - 1);
// factorial(6) -> 720

⬆ back to top

fibonacci

指定一个长度,输出斐波那契数列

1
2
3
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]

⬆ back to top

gcd

计算两个数字之间的最大公约数。

1
2
const gcd = (x, y) => !y ? x : gcd(y, x % y);
// gcd (8, 36) -> 4

⬆ back to top

hammingDistance

计算两个值的Hamming距离.

1
2
3
const hammingDistance = (num1, num2) =>
((num1 ^ num2).toString(2).match(/1/g) || '').length;
// hammingDistance(2,3) -> 1

⬆ back to top

isDivisible

检查第一个数字是否可被第二个数字整除.

1
2
const isDivisible = (dividend, divisor) => dividend % divisor === 0;
// isDivisible(6,3) -> true

⬆ back to top

isEven

检查数字是否为偶数

1
2
const isEven = num => num % 2 === 0;
// isEven(3) -> false

⬆ back to top

lcm

计算两个数字的最小公倍数.

1
2
3
4
5
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) -> 84

⬆ back to top

median

返回数组的中位数

1
2
3
4
5
6
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]) -> 3.5

⬆ back to top

palindrome

判断给定字符串是否是回文字符串(回文字符串是正读和反读都一样的字符串,比如“level”或者“noon”)

1
2
3
4
5
const palindrome = str => {
const s = str.toLowerCase().replace(/[\W_]/g,'');
return s === s.split('').reverse().join('');
}
// palindrome('taco cat') -> true

⬆ back to top

percentile

使用百分位数公式来计算给定数组中有多少数字小于或等于给定值。

1
2
3
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) -> 55

⬆ back to top

powerset

输出给定数组的所有子集

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

⬆ back to top

randomIntegerInRange

返回指定范围内的随机整数

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

⬆ back to top

randomNumberInRange

返回指定范围内的随机数

1
2
const randomNumberInRange = (min, max) => Math.random() * (max - min) + min;
// randomNumberInRange(2,10) -> 6.0211363285087005

⬆ back to top

round

将数字四舍五入到指定的数字位数.

1
2
const round = (n, decimals=0) => Number(`${Math.round(`${n}e${decimals}`)}e-${decimals}`);
// round(1.005, 2) -> 1.01

⬆ back to top

standardDeviation

返回数组的标准差

1
2
3
4
5
6
7
8
9
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)

⬆ back to top

Media

speechSynthesis

语音合成 (实验特性).

详情查看 SpeechSynthesisUtterance interface of the Web Speech API.

1
2
3
4
5
6
const speechSynthesis = message => {
const msg = new SpeechSynthesisUtterance(message);
msg.voice = window.speechSynthesis.getVoices()[0];
window.speechSynthesis.speak(msg);
};
// speechSynthesis('Hello, World') -> plays the message

⬆ back to top

Node

JSONToFile

将一个JSON对象转换为文件.

1
2
3
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'

⬆ back to top

readFileLines

读取指定的文件并且根据行生成数组

1
2
3
4
5
6
7
8
9
10
11
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']
*/

⬆ back to top

Object

cleanObj

移除对象中除去给定的属性名之外的属性

1
2
3
4
5
6
7
8
9
10
11
12
13
14
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];
}
})
}
/*
const testObj = {a: 1, b: 2, children: {a: 1, b: 2}}
cleanObj(testObj, ["a"],"children")
console.log(testObj)// { a: 1, children : { a: 1}}
*/

⬆ back to top

objectFromPairs

根据给定的键值对生成对象

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

⬆ back to top

objectToPairs

转换一个对象为数组

1
2
const objectToPairs = obj => Object.keys(obj).map(k => [k, obj[k]]);
// objectToPairs({a: 1, b: 2}) -> [['a',1],['b',2]])

⬆ back to top

shallowClone

创建一个对象的浅拷贝.

1
2
3
4
5
6
const shallowClone = obj => Object.assign({}, obj);
/*
const a = { x: true, y: 1 };
const b = shallowClone(a);
a === b -> false
*/

⬆ back to top

truthCheckCollection

检查某个属性名是否在一个数组中都存在

1
2
truthCheckCollection = (collection, pre) => (collection.every(obj => obj[pre]));
// truthCheckCollection([{"user": "Tinky-Winky", "sex": "male"}, {"user": "Dipsy", "sex": "male"}], "sex") -> true

⬆ back to top

String

anagrams

生成一个字符串的所有字符排列组合(包含重复)

1
2
3
4
5
6
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']

⬆ back to top

Capitalize

将给定字符串首字母大写.

1
2
3
4
const capitalize = ([first,...rest], lowerRest = false) =>
first.toUpperCase() + (lowerRest ? rest.join('').toLowerCase() : rest.join(''));
// capitalize('myName') -> 'MyName'
// capitalize('myName', true) -> 'Myname'

⬆ back to top

capitalizeEveryWord

将给定字符串的每个单词首字母大写.

1
2
const capitalizeEveryWord = str => str.replace(/\b[a-z]/g, char => char.toUpperCase());
// capitalizeEveryWord('hello world!') -> 'Hello World!'

⬆ back to top

escapeRegExp

转义字符串以便在正则表达式中使用

1
2
const escapeRegExp = str => str.replace(/[.*+?^${}()|[\]\\]/g, '\\$&');
// escapeRegExp('(test)') -> \\(test\\)

⬆ back to top

fromCamelCase

把camelcase字符串转换成其他格式

1
2
3
4
5
6
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'

⬆ back to top

reverseString

反转字符串

1
2
const reverseString = str => [...str].reverse().join('');
// reverseString('foobar') -> 'raboof'

⬆ back to top

sortCharactersInString

按照字母顺序重新排列字符串

1
2
3
const sortCharactersInString = str =>
str.split('').sort((a, b) => a.localeCompare(b)).join('');
// sortCharactersInString('cabbage') -> 'aabbceg'

⬆ back to top

toCamelCase

把一个字符串转换为camelcase.

1
2
3
4
5
6
const toCamelCase = str =>
str.replace(/^([A-Z])|[\s-_]+(\w)/g, (match, p1, p2, offset) => p2 ? p2.toUpperCase() : p1.toLowerCase());
// 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'

⬆ back to top

truncateString

根据指定长度截取字符串

1
2
3
const truncateString = (str, num) =>
str.length > num ? str.slice(0, num > 3 ? num - 3 : num) + '...' : str;
// truncateString('boomerang', 7) -> 'boom...'

⬆ back to top

Utility

coalesce

返回第一个不为null/undefined的参数

1
2
const coalesce = (...args) => args.find(_ => ![undefined, null].includes(_))
// coalesce(null,undefined,"",NaN, "Waldo") -> ""

⬆ back to top

coalesceFactory

实现自定义coalesce函数

1
2
3
const coalesceFactory = valid => (...args) => args.find(valid);
// const customCoalesce = coalesceFactory(_ => ![null, undefined, "", NaN].includes(_))
// customCoalesce(undefined, null, NaN, "", "Waldo") //-> "Waldo"

⬆ back to top

extendHex

将3位数的颜色代码扩展为6位数的颜色代码

1
2
3
4
const extendHex = shortHex =>
'#' + shortHex.slice(shortHex.startsWith('#') ? 1 : 0).split('').map(x => x+x).join('')
// extendHex('#03f') -> '#0033ff'
// extendHex('05a') -> '#0055aa'

⬆ back to top

getType

获取一个值的原生类型.

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

⬆ back to top

hexToRGB

将hex色值转换为RGB

1
2
3
4
5
6
7
8
const hexToRgb = hex => {
const extendHex = shortHex =>
'#' + shortHex.slice(shortHex.startsWith('#') ? 1 : 0).split('').map(x => x+x).join('');
const extendedHex = hex.slice(hex.startsWith('#') ? 1 : 0).length === 3 ? extendHex(hex) : hex;
return `rgb(${parseInt(extendedHex.slice(1), 16) >> 16}, ${(parseInt(extendedHex.slice(1), 16) & 0x00ff00) >> 8}, ${parseInt(extendedHex.slice(1), 16) & 0x0000ff})`;
}
// hexToRgb('#27ae60') -> 'rgb(39, 174, 96)'
// hexToRgb('#acd') -> 'rgb(170, 204, 221)'

⬆ back to top

isArray

检查给定对象是否是数组

1
2
3
const isArray = val => !!val && Array.isArray(val);
// isArray(null) -> false
// isArray([1]) -> true

⬆ back to top

isBoolean

检查给定对象是否是布尔值

1
2
3
const isBoolean = val => typeof val === 'boolean';
// isBoolean(null) -> false
// isBoolean(false) -> true

⬆ back to top

isFunction

检查给定对象是否是方法

1
2
3
const isFunction = val => val && typeof val === 'function';
// isFunction('x') -> false
// isFunction(x => x) -> true

⬆ back to top

isNumber

检查给定对象是否是数字

1
2
3
const isNumber = val => typeof val === 'number';
// isNumber('1') -> false
// isNumber(1) -> true

⬆ back to top

isString

检查给定对象是否是字符串

1
2
3
const isString = val => typeof val === 'string';
// isString(10) -> false
// isString('10') -> true

⬆ back to top

isSymbol

检查给定对象是否是symbol.

1
2
3
const isSymbol = val => typeof val === 'symbol';
// isSymbol('x') -> false
// isSymbol(Symbol('x')) -> true

⬆ back to top

RGBToHex

将RGB色值转换为Hex

1
2
const RGBToHex = (r, g, b) => ((r << 16) + (g << 8) + b).toString(16).padStart(6, '0');
// RGBToHex(255, 165, 1) -> 'ffa501'

⬆ back to top

timeTaken

计算函数执行时间

1
2
3
4
5
6
const timeTaken = callback => {
console.time('timeTaken'); const r = callback();
console.timeEnd('timeTaken'); return r;
};
// timeTaken(() => Math.pow(2, 10)) -> 1024
// (logged): timeTaken: 0.02099609375ms

⬆ back to top

toOrdinalSuffix

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.

1
2
3
4
5
6
7
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"

⬆ back to top

UUIDGenerator

生成UUID.

1
2
3
4
5
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'

⬆ back to top

validateEmail

验证是否为邮箱

1
2
3
const validateEmail = str =>
/^(([^<>()\[\]\\.,;:\s@"]+(\.[^<>()\[\]\\.,;:\s@"]+)*)|(".+"))@((\[[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\])|(([a-zA-Z\-0-9]+\.)+[a-zA-Z]{2,}))$/.test(str);
// validateEmail(mymail@gmail.com) -> true

⬆ back to top

validateNumber

验证是否为数字

1
2
const validateNumber = n => !isNaN(parseFloat(n)) && isFinite(n) && Number(n) == n;
// validateNumber('10') -> true

⬆ back to top

Credits

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