DOM

1、检查元素是否被聚焦

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

2、获取元素的所有兄弟元素

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

3、获取选定的文本

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

4、返回上一个页面

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

5、清除所有 cookie

const clearCookies = () => document.cookie.split(';').forEach((c) =>(document.cookie = c.replace(/^ +/, '').replace(/=.*/, `=;expires=${new Date().toUTCString()};path=/`)));

6、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

1、比较两个数组

// `a` and `b` are arrays
const isEqual = (a, b) => JSON.stringify(a) === JSON.stringify(b);
// Or
const isEqual = (a, b) => a.length === b.length && a.every((v, i) => v === b[i]);
// Examples
isEqual([1, 2, 3], [1, 2, 3]); // true
isEqual([1, 2, 3], [1, '2', 3]); // false

2、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]));
// Example
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' }
}
*/

3、按对象数组的属性计数

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

4、检查数组是否为空

const isNotEmpty = (arr) => Array.isArray(arr) && Object.keys(arr).length > 0;
// Examples
isNotEmpty([]); // false
isNotEmpty([1, 2, 3]); // true

对象

1、检查多个对象是否相等

const isEqual = (...objects) => objects.every((obj) => JSON.stringify(obj) === JSON.stringify(objects[0]));
// Examples
isEqual({ foo: 'bar' }, { foo: 'bar' }); // true
isEqual({ foo: 'bar' }, { bar: 'foo' }); // false

2、从对象数组中提取属性的值

const pluck = (objs, property) => objs.map((obj) => obj[property]);
// Example
pluck([
{ name: 'John', age: 20 },
{ name: 'Smith', age: 25 },
{ name: 'Peter', age: 30 },
],
'name');
// ['John', 'Smith', 'Peter']

3、反转对象的键和值

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

4、从对象中删除所有空和未定义的属性

const removeNullUndefined = (obj) => 
Object.entries(obj)
.reduce((a, [k, v]) => (v == null ? a : ((a[k] = v), a)), {});
// Or
const removeNullUndefined = (obj) =>
Object.entries(obj)
.filter(([_, v]) => v != null)
.reduce((acc, [k, v]) => ({ ...acc, [k]: v }), {});
// Or
const removeNullUndefined = (obj) => Object.fromEntries(Object.entries(obj).filter(([_, v]) => v != null));
// Example
removeNullUndefined({
foo: null,
bar: undefined,
fuzz: 42}); 
// { fuzz: 42 }

5、按属性对对象进行排序

const sort = (obj) =>
Object.keys(obj)
.sort()
.reduce((p, c) => ((p[c] = obj[c]), p), {});
// Example
const colors = {
white: '#ffffff',
black: '#000000',
red: '#ff0000',
green: '#008000',
blue: '#0000ff',
};
sort(colors);
/*
{
black: '#000000',
blue: '#0000ff',
green: '#008000',
red: '#ff0000',
white: '#ffffff',
}
*/

6、检查一个对象是否是一个 Promise

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

7、检查对象是否为数组

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

字符串

1、检查路径是否是相对的

const isRelative = (path) => !/^([a-z]+:)?[\\/]/i.test(path);
// Examples
isRelative('/foo/bar/baz'); // false
isRelative('C:\\foo\\bar\\baz'); // false
isRelative('foo/bar/baz.txt'); // true
isRelative('foo.md'); // true

2、使字符串的第一个字符小写

const lowercaseFirst = (str) => `${str.charAt(0).toLowerCase()}${str.slice(1)}`;
// Example
lowercaseFirst('Hello World'); // 'hello World'

3、重复一个字符串

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

4、检查字符串是否为十六进制颜色

const isHexColor = (color) => /^#([0-9A-F]{3}|[0-9A-F]{4}|[0-9A-F]{6}|[0-9A-F]{8})$/i.test(color);
// Examples
isHexColor('#012'); // true
isHexColor('#A1B2C3'); // true
isHexColor('012'); // false
isHexColor('#GHIJKL'); // false

日期

1、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'}`;
// Examples
suffixAmPm(0); // '12am'
suffixAmPm(5); // '5am'
suffixAmPm(12); // '12pm'
suffixAmPm(15); // '3pm'
suffixAmPm(23); // '11pm'

2、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));
// Example
diffDays(new Date('2014-12-19'), new Date('2020-01-01')); // 1839

3、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

其他的

1、检查代码是否在 Node.js 中运行

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

2、检查代码是否在浏览器中运行

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

3、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 }),{});
// Examples
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" }

4、检测暗模式

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

5、交换两个变量

[a, b] = [b, a];

6、复制到剪贴板

const copyToClipboard = (text) => navigator.clipboard.writeText(text);
// Example
copyToClipboard("Hello World");

7、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);
// Example
rgbToHex(0, 51, 255); // #0033ff

8、生成随机十六进制颜色

const randomColor = () => `#${Math.random().toString(16).slice(2, 8).padEnd(6, '0')}`;
// Or
const randomColor = () => `#${(~~(Math.random() * (1 << 24))).toString(16)}`;

9、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('.');
// Example
randomIp(); // 175.89.174.131

10、使用 Node crypto 模块生成随机字符串

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