DOM

检查一个元素是否被聚焦

const hasFocus = (ele) => ele === document.activeElement

获取一个元素的所有兄弟元素

const siblings = (ele) => 
  .slice.call(ele.parentNode.children).filter((child) => child !== ele);

获取选中文本

const getSelectedText = () => window.getSelection().toString();

回到上一页

history.back();
// Or
history.go(-1);

清除所有 cookies

const cookies = document.cookie.split(';').map((item) => 
item.split('=')).reduce((acc, [k, v]) => (acc[k.trim().replace('"', '')] = v) && acc, );

将 cookie 转换为对象

const cookies = document.cookie.split(';').map((item) => item.split('=')).reduce((acc, [k, v]) => (acc[k.trim().replace('"', '')] = v) && acc, );

数组

比较两个数组

// `a` 和 `b` 都是数组
const isEqual = (a, b) => JSON.stringify(a) === JSON.stringify(b);

// 或者
const isEqual = (a, b) => a.length === b.length && 
  a.every((v, i) => v === b[i]);

// 事例
isEqual([1, 2, 3], [1, 2, 3]); // true
isEqual([1, 2, 3], [1, '2', 3]); // false

将对象数组转换为单个对象

const toObject = (arr, key) => arr.reduce((a, b) => ( ...a, [b[key]]: b ), );
// Or
const toObject = (arr, key) => Object.fromEntries(arr.map((it) => [it[key], it]));

// 事例
toObject([
 id: '1', name: 'Alpha', gender: 'Male' ,
 id: '2', name: 'Bravo', gender: 'Male' ,
 id: '3', name: 'Charlie', gender: 'Female' ],
'id');
/*

'1':  id: '1', name: 'Alpha', gender: 'Male' ,
'2':  id: '2', name: 'Bravo', gender: 'Male' ,
'3':  id: '3', name: 'Charlie', gender: 'Female' 

*/

根据对象数组的属性进行计数

const countBy = (arr, prop) => arr.reduce((prev, curr) => ((prev[curr[prop]] = ++prev[curr[prop]] || 1), prev), );

// 事例
countBy([
 branch: 'audi', model: 'q8', year: '2019' ,
 branch: 'audi', model: 'rs7', year: '2020' ,
 branch: 'ford', model: 'mustang', year: '2019' ,
 branch: 'ford', model: 'explorer', year: '2020' ,
 branch: 'bmw', model: 'x7', year: '2020' ,
],
'branch');

//  'audi': 2, 'ford': 2, 'bmw': 1 

检查数组是否为空

const isNotEmpty = (arr) => Array.isArray(arr) && Object.keys(arr).length > 0;

// 事例
isNotEmpty([]); // false
isNotEmpty([1, 2, 3]); // true

对象

检查多个对象是否相等

const isEqual = (...objects) => objects.every((obj) =>
  JSON.stringify(obj) === JSON.stringify(objects[0]));
// 事例

console.log(isEqual( foo: 'bar' ,  foo: 'bar' )); // true
console.log(isEqual( foo: 'bar' ,  bar: 'foo' )); // false

从对象数组中提取指定属性的值

const pluck = (objs, property) => objs.map((obj) => obj[property]);
// Example
const aa = pluck([
 name: '小2', age: 20 ,
 name: '大2', age: 25 ,
 name: '王22', age: 30 ,
],
'name');
// [ '小2', '大2', '王22' ]

反转对象的键和值

const invert = (obj) => Object.keys(obj).reduce((res, k) => Object.assign(res,  [obj[k]]: k ), );
// 或
const invert = (obj) => Object.fromEntries(Object.entries(obj).map(([k, v]) => [v, k]));
// 事例
invert( a: '1', b: '2', c: '3' ); //  1: 'a', 2: 'b', 3: 'c' 

从对象中删除所有 null 和 undefined 的属性

const removeNullUndefined = (obj) => 
  Object.entries(obj)
   .reduce((a, [k, v]) => (v == null ? a : ((a[k] = v), a)), );

// 或

const removeNullUndefined = (obj) =>
  Object.entries(obj)
  .filter(([_, v]) => v != null)
  .reduce((acc, [k, v]) => ( ...acc, [k]: v ), );

// 或

const removeNullUndefined = (obj) => 
    Object.fromEntries(Object.entries(obj).filter(([_, v]) => v != null));

// 例子
removeNullUndefined(
  foo: null,
  bar: undefined,
  fuzz: 42
); 
//  fuzz: 42 

根据对象的属性对其进行排序

Object.keys(obj)
  .sort()
  .reduce((p, c) => ((p[c] = obj[c]), p), );

// 事例
const colors = 
  white: '#ffffff',
  black: '#000000',
  red: '#ff0000',
  green: '#008000',
  blue: '#0000ff',
;

sort(colors);

/*

  black: '#000000',
  blue: '#0000ff',
  green: '#008000',
  red: '#ff0000',
  white: '#ffffff',

*/

检查一个对象是否是Promise

const isPromise = (obj) =>
!!obj && (typeof obj === 'object' || typeof obj === 'function') && 
typeof obj.then === 'function';

检查一个对象是否是一个数组

  const isArray = (obj) => Array.isArray(obj);

字符串

检查路径是否是相对路径

const isRelative = (path) => !/^([a-z]+:)?[\\\\/]/i.test(path);

// 例子
isRelative('/foo/bar/baz'); // false
isRelative('C:\\\\foo\\\\bar\\\\baz'); // false
isRelative('foo/bar/baz.txt'); // true
isRelative('foo.md'); // true

将字符串的第一个字符改为小写

const lowercaseFirst = (str) => `$str.charAt(0).toLowerCase()$str.slice(1)`;

// 例子
lowercaseFirst('Hello World'); // 'hello World'

重复一个字符串

const repeat = (str, numberOfTimes) => str.repeat(numberOfTimes);

// 例子
repeat('ab', 3)
// ababab

Dates

给一个小时添加“am/pm”后缀

// `h` is an hour number between 0 and 23
const suffixAmPm = (h) => `$h % 12 === 0 ? 12 : h % 12$h < 12 ? 'am' : 'pm'`;

// 例子
suffixAmPm(0); // '12am'
suffixAmPm(5); // '5am'
suffixAmPm(12); // '12pm'
suffixAmPm(15); // '3pm'
suffixAmPm(23); // '11pm'

计算两个日期之间的不同天数

const diffDays = (date, otherDate) => Math.ceil(Math.abs(date - otherDate) / (1000 * 60 * 60 * 24));

// 例子
diffDays(new Date('2014-12-19'), new Date('2020-01-01')); // 1839

检查日期是否有效

const isDateValid = (...val) => !Number.isNaN(new Date(...val).valueOf());

isDateValid("December 17, 1995 03:24:00"); // true

其它

检查代码是否在Node.js中运行

const isNode = typeof process !== 'undefined' && process.versions != null && 
  process.versions.node != null;

检查代码是否在浏览器中运行

const isBrowser = typeof window === 'object' && typeof document === 'object';

将URL参数转换为对象

const getUrlParams = (query) =>Array.from(new   URLSearchParams(query)).reduce((p, [k, v]) => Object.assign(, p,  [k]: p[k]   ? (Array.isArray(p[k]) ? p[k] : [p[k]]).concat(v) : v ),);

// 例子
getUrlParams(location.search); // Get the parameters of the current URL
getUrlParams('foo=Foo&bar=Bar'); //  foo: "Foo", bar: "Bar" 

// Duplicate key
getUrlParams('foo=Foo&foo=Fuzz&bar=Bar'); //  foo: ["Foo", "Fuzz"], bar: "Bar" 

黑暗检测模式

const isDarkMode = window.matchMedia && window.matchMedia('(prefers-color-scheme: dark)').matches;

拷贝到剪切板

const copyToClipboard = (text) => 
  navigator.clipboard.writeText(text);

// 例子
copyToClipboard("Hello World");

将RGB转换为十六进制

const rgbToHex = (r, g, b) =>
   "#" + ((1 << 24) + (r << 16) + (g << 8) + b).toString(16).slice(1);

// 例子
rgbToHex(0, 51, 255); // #0033ff

生成一个随机的十六进制颜色

const randomColor = () => `#$Math.random().toString(16).slice(2, 8).padEnd(6, '0')`;

// 或者

const randomColor = () => `#$(~~(Math.random() * (1 << 24))).toString(16)`;

生成随机IP地址

const randomIp = () => Array(4).fill(0)
.map((_, i) => Math.floor(Math.random() * 255) + (i === 0 ? 1 : 0))
.join('.');

// 例子
randomIp(); // 175.89.174.131

使用 Node crypto 模块生成随机字符串

const randomStr = () => require('crypto').randomBytes(32).toString('hex');