1 String技巧
2 Number技巧
3 Boolean技巧
4 Array技巧
5 Object技巧
6 Function技巧
7 DOM技巧
把值转换成String的5个方法
你最了解你的程序，因此你应该选择最适合你的方式。
const value = 12345;
// Concat Empty String
value + '';
// Template Strings
`${value}`;
// JSON.stringify
JSON.stringify(value);
// toString()
value.toString();
// String()
String(value);
// RESULT
// '12345'
字符串插值
在用例中，如果正在构建一个基于模板的helper组件，那么这一点就会非常突出，它使动态模板连接容易得多。
const user = {
name: 'John',
surname: 'Doe',
details: {
email: '[email protected]',
displayName: 'SuperCoolJohn',
joined: '2016-05-05',
image: 'path-to-the-image',
followers: 45
}
}
const printUserInfo = (user) => {
const text = `The user is ${user.name} ${user.surname}. Email: ${user.details.email}. Display Name: ${user.details.displayName}. ${user.name} has ${user.details.followers} followers.`
console.log(text);
}
printUserInfo(user);
// outputs 'The user is John Doe. Email: [email protected]. Display Name: SuperCoolJohn. John has 45 followers.'
格式化金额
const thousandNum = num => num.toString().replace(/\B(?=(\d{3})+(?!\d))/g, ',');
const money = thousandNum(20190214);
生成随机ID
const randomId = len => Math.random().toString(36).substr(3, len);
const id = randomId(10);
console.log(id) // jg7zpgiqva
生成随机HEX色值
const randomColor = () => "#" + Math.floor(Math.random() * 0xffffff).toString(16).padEnd(6, "0");
const color = randomColor();
// color => "#f03665"
操作URL查询参数
const params = new URLSearchParams(location.search.replace(/\?/ig, '')); // location.search = "?name=young&sex=male"
params.has("young"); // true
params.get("sex"); // "male"
生成星级评分
const startScore = rate => "★★★★★☆☆☆☆☆".slice(5 - rate, 10 - rate);
const start = startScore(3);
// start => "★★★"
取整：代替正数的Math.floor()，代替负数的Math.ceil()
const num1 = ~~ 1.69;
const num2 = 1.69 | 0;
const num3 = 1.69 >> 0;
// num1 num2 num3 => 1 1 1
补零
const fillZero = (num, len) => num.toString().padStart(len, '0');
const num = fillZero(169, 5);
// num => "00169"
转数值：只对null、''、false、数值字符串有效
const num1 = +null;
const num2 = +'';
const num3 = +false;
const num4 = +'169';
// num1 num2 num3 num4 => 0 0 0 169
时间戳
const timestamp = +new Date('2019-02-14');
// timestamp => 1550102400000
精确小数
const roundNum = (num, decimal) => Math.round(num * 10 ** decimal) / 10 ** decimal;
const num = roundNum(1.69, 1);
// num => 1.7
判断奇偶
const oddEven = num => !!(num & 1) ? 'odd' : 'even';
const num = oddEven(2);
// num => 'even'
// 或
const isOdd = num => {num % 2}
// 或
const isOdd = num => num & 1
取最小最大值
const arr = [0, 1, 2];
const min = Math.min(...arr);
const max = Math.max(...arr);
// min max => 0 2
生成范围随机数
const randomNum = (min, max) => Math.floor(Math.random() * (max - min + 1)) + min;
const num = randomNum(1, 10);
短路运算符
const a = d && 1; // 满足条件赋值：取假运算，从左到右依次判断，遇到假值返回假值，后面不再执行，否则返回最后一个真值
const b = d || 1; // 默认赋值：取真运算，从左到右依次判断，遇到真值返回真值，后面不再执行，否则返回最后一个假值
const c = !d; // 取假赋值：单个表达式转换为true则返回false，否则返回true
判断数据类型：undefined、null、string、number、boolean、array、object、symbol、date、regexp、function、asyncfunction、arguments、set、map、weakset、weakmap
function dataType(tgt, type) {
const dataType = Object.prototype.toString.call(tgt).replace(/\[object /g, '').replace(/\]/g, '').toLowerCase();
return type ? dataType === type : dataType;
}
dataType('young'); // "string"
dataType(20190214); // "number"
dataType(true); // "boolean"
dataType([], 'array'); // true
dataType({}, 'array'); // false
是否为空数组
const arr = [];
const flag = Array.isArray(arr) && !arr.length;
// flag => true
是否为空对象
function dataType(tgt, type) {
const dataType = Object.prototype.toString.call(tgt).replace(/\[object /g, "").replace(/\]/g, "").toLowerCase();
return type ? dataType === type : dataType;
}
const obj = {};
const flag = dataType(obj, 'object') && !Object.keys(obj).length;
// flag => true
满足条件时执行
function Func () {
// doing...
}
const flagA = true; // 条件A
const flagB = false; // 条件B
(flagA || flagB) && Func(); // 满足A或B时执行
(flagA || !flagB) && Func(); // 满足A或不满足B时执行
flagA && flagB && Func(); // 同时满足A和B时执行
flagA && !flagB && Func(); // 满足A且不满足B时执行
为非假值时执行
function Func () {
// doing...
}
const flag = false; // undefined、null、''、0、false、NaN
!flag && Func();
数组不为空时执行
function Func () {
// doing...
}
const arr = [0, 1, 2];
arr.length && Func();
对象不为空时执行
function Func () {
// doing...
}
const obj = {a: 0, b: 1, c: 2};
Object.keys(obj).length && Func();
函数退出代替条件分支退出
function Func () {
// doing...
}
const flag = true;
if (flag) {
Func();
return false;
}
// 换成
if (flag) {
return Func();
}
switch/case使用区间
const age = 26;
switch (true) {
case isNaN(age):
console.log("not a number");
break;
case (age < 18):
console.log("under age");
break;
case (age >= 18):
console.log("adult");
break;
default:
console.log("please set your age");
break;
}
获取数组唯一值
ES6 提供了从数组中提取唯一值的两种非常简洁的方法。不幸的是，它们不能很好地处理非基本类型的数组。在本文中，主要关注基本数据类型。
const cars = ['Mazda', 'Ford', 'Renault', 'Opel', 'Mazda'];
const uniqueWithArrayFrom = Array.from(new Set(cars));
console.log(uniqueWithArrayFrom); // outputs ['Mazda', 'Ford', 'Renault', 'Opel']
const uniqueWithSpreadOperator = [...new Set(cars)];
console.log(uniqueWithSpreadOperator); // outputs ['Mazda', 'Ford', 'Renault', 'Opel']
使用展开运算符合并对象和对象数组
对象合并是很常见的事情，我们可以使用新的ES6特性来更好，更简洁的处理合并的过程。
// merging objects
const product = { name: 'Milk', packaging: 'Plastic', price: '5$' }
const manufacturer = { name: 'Company Name', address: 'The Company Address' }
const productManufacturer = { ...product, ...manufacturer };
console.log(productManufacturer);
// outputs { name: "Company Name", packaging: "Plastic", price: "5$", address: "The Company Address" }
// merging an array of objects into one
const cities = [
{ name: 'Paris', visited: 'no' },
{ name: 'Lyon', visited: 'no' },
{ name: 'Marseille', visited: 'yes' },
{ name: 'Rome', visited: 'yes' },
{ name: 'Milan', visited: 'no' },
{ name: 'Palermo', visited: 'yes' },
{ name: 'Genoa', visited: 'yes' },
{ name: 'Berlin', visited: 'no' },
{ name: 'Hamburg', visited: 'yes' },
{ name: 'New York', visited: 'yes' }
];
const result = cities.reduce((accumulator, item) => {
return {
...accumulator,
[item.name]: item.visited
}
}, {});
console.log(result);
/* outputs
Berlin: "no"
Genoa: "yes"
Hamburg: "yes"
Lyon: "no"
Marseille: "yes"
Milan: "no"
New York: "yes"
Palermo: "yes"
Paris: "no"
Rome: "yes"
*/
数组 map 的方法 (不使用Array.Map)
另一种数组 map 的实现的方式，不用 Array.map。
Array.from 还可以接受第二个参数，作用类似于数组的map方法，用来对每个元素进行处理，将处理后的值放入返回的数组。如下：
const cities = [
{ name: 'Paris', visited: 'no' },
{ name: 'Lyon', visited: 'no' },
{ name: 'Marseille', visited: 'yes' },
{ name: 'Rome', visited: 'yes' },
{ name: 'Milan', visited: 'no' },
{ name: 'Palermo', visited: 'yes' },
{ name: 'Genoa', visited: 'yes' },
{ name: 'Berlin', visited: 'no' },
{ name: 'Hamburg', visited: 'yes' },
{ name: 'New York', visited: 'yes' }
];
const cityNames = Array.from(cities, ({ name}) => name);
console.log(cityNames);
// outputs ["Paris", "Lyon", "Marseille", "Rome", "Milan", "Palermo", "Genoa", "Berlin", "Hamburg", "New York"]
克隆数组
const arr1 = [0, 1, 2];
const arr2 = [...arr1];
// arr2 => [0, 1, 2]
合并数组
const arr1 = [0, 1, 2];
const arr2 = [3, 4, 5];
const arr = [...arr1, ...arr2];
// arr => [0, 1, 2, 3, 4, 5];
去重数组
const arr = [...new Set([0, 1, 1, null, null])];
// arr => [0, 1, null]
混淆数组
const arr = [0, 1, 2, 3, 4, 5].slice().sort(() => Math.random() - .5);
// arr => [3, 4, 0, 5, 1, 2]
截断数组
const arr = [0, 1, 2];
arr.length = 2;
// arr => [0, 1]
交换赋值
let a = 0;
let b = 1;
[a, b] = [b, a];
// a b => 1 0
// 或 只能是整数才能使用该方法
let a = 0;
let b = 1;
a ^= b;
b ^= a;
a ^= b;
过滤空值：undefined、null、''、0、false、NaN
const arr = [undefined, null, '', 0, false, NaN, 1, 2].filter(Boolean);
// arr => [1, 2]
数组首部插入成员
let arr = [1, 2]; // 以下方法任选一种
arr.unshift(0);
// 或
arr = [0].concat(arr);
// 或
arr = [0, ...arr];
// arr => [0, 1, 2]
数组尾部插入成员
let arr = [0, 1]; // 以下方法任选一种
arr.push(2);
// 或
arr.concat(2);
// 或
arr[arr.length] = 2;
// 或
arr = [...arr, 2];
// arr => [0, 1, 2]
统计数组成员个数
const arr = [0, 1, 1, 2, 2, 2];
const count = arr.reduce((t, c) => {
t[c] = t[c] ? ++ t[c] : 1;
return t;
}, {});
// count => { 0: 1, 1: 2, 2: 3 }
解构数组成员嵌套
const arr = [0, 1, [2, 3, [4, 5]]];
const [a, b, [c, d, [e, f]]] = arr;
// a b c d e f => 0 1 2 3 4 5
解构数组成员别名
const arr = [0, 1, 2];
const { 0: a, 1: b, 2: c } = arr;
// a b c => 0 1 2
解构数组成员默认值
const arr = [0, 1, 2];
const [a, b, c = 3, d = 4] = arr;
// a b c d => 0 1 2 4
获取随机数组成员
const arr = [0, 1, 2, 3, 4, 5];
const randomItem = arr[Math.floor(Math.random() * arr.length)];
// randomItem => 1
创建指定长度数组
const arr = [...new Array(3).keys()];
// arr => [0, 1, 2]
创建指定长度且值相等的数组
const arr = new Array(3).fill(0);
// arr => [0, 0, 0]
reduce代替map和filter
const _arr = [0, 1, 2];
// map
const arr = _arr.map(v => v * 2);
const arr = _arr.reduce((t, c) => {
t.push(c * 2);
return t;
}, []);
// arr => [0, 2, 4]
// filter
const arr = _arr.filter(v => v > 0);
const arr = _arr.reduce((t, c) => {
c > 0 && t.push(c);
return t;
}, []);
// arr => [1, 2]
// map和filter
const arr = _arr.map(v => v * 2).filter(v => v > 2);
const arr = _arr.reduce((t, c) => {
c = c * 2;
c > 2 && t.push(c);
return t;
}, []);
// arr => [4]
克隆对象
const obj1 = {a: 0, b: 1, c: 2}; // 以下方法任选一种
const obj2 = {...obj1};
const obj2 = JSON.parse(JSON.stringify(obj1));
// obj2 => { a: 0, b: 1, c: 2 }
合并对象
const obj1 = {a: 0, b: 1, c: 2};
const obj2 = {c: 3, d: 4, e: 5};
const obj = { ...obj1, ...obj2 };
// obj => { a: 0, b: 1, c: 3, d: 4, e: 5 }
对象字面量：获取环境变量时必用此方法，用它一直爽，一直用它一直爽
const env = 'prod';
const link = {
dev: 'Development Address',
test: 'Testing Address',
prod: 'Production Address'
}[env];
// link => "Production Address"
对象变量属性
const flag = false;
const obj = {
a: 0,
b: 1,
[flag ? 'c' : 'd']: 2
};
// obj => { a: 0, b: 1, d: 2 }
删除对象无用属性
const obj = {a: 0, b: 1, c: 2}; // 只想拿b和c
const {a, ...rest} = obj;
// rest => { b: 1, c: 2 }
解构对象属性嵌套
const obj = {a: 0, b: 1, c: {d: 2, e: 3}};
const {c: {d, e}} = obj;
// d e => 2 3
解构对象属性别名
const obj = {a: 0, b: 1, c: 2};
const {a, b: d, c: e} = obj;
// a d e => 0 1 2
解构对象属性默认值
const obj = {a: 0, b: 1, c: 2};
const {a, b = 2, d = 3} = obj;
// a b d => 0 1 3
有条件的对象属性
不再需要根据一个条件创建两个不同的对象，可以使用展开运算符号来处理。
let getUser = (emailIncluded) => {
return {
name: 'John',
surname: 'Doe',
...emailIncluded && {email : '[email protected]'}
}
}
const user = getUser(true);
console.log(user); // outputs {name: 'John', surname: 'Doe', email: '[email protected]'}
const userWithoutEmail = getUser(false);
console.log(userWithoutEmail); // outputs {name: 'John', surname: 'Doe'}
解构原始数据
有时候一个对象包含很多属性，而我们只需要其中的几个，这里可以使用解构方式来提取我们需要的属性。如一个用户对象内容如下：
const rawUser = {
name: 'John',
surname: 'Doe',
email: '[email protected]',
displayName: 'SuperCoolJohn',
joined: '2016-05-05',
image: 'path-to-the-image',
followers: 45,
...
}
我们需要提取出两个部分，分别是用户及用户信息，这时可以这样做:
let user = {}, userDetails = {};
({ name: user.name, surname: user.surname, ...userDetails } = rawUser);
console.log(user); // outputs { name: "John", surname: "Doe" }
console.log(userDetails); // outputs { email: "[email protected]", displayName: "SuperCoolJohn", joined: "2016-05-05", image: "path-to-the-image", followers: 45 }
动态属性名
早期，如果属性名需要是动态的，我们首先必须声明一个对象，然后分配一个属性。这些日子已经过去了，有了ES6特性，我们可以做到这一点。
const dynamic = 'email';
let user = {
name: 'John',
[dynamic]: '[email protected]'
}
console.log(user); // outputs { name: "John", email: "[email protected]" }
函数自执行
const Func = function() {}(); // 常用
(function() {})(); // 常用
(function() {}()); // 常用
[function() {}()];
+ function() {}();
- function() {}();
~ function() {}();
! function() {}();
new function() {};
new function() {}();
void function() {}();
typeof function() {}();
delete function() {}();
1, function() {}();
1 ^ function() {}();
1 > function() {}();
隐式返回值：只能用于单语句返回值箭头函数，如果返回值是对象必须使用()包住
const Func = function(name) {
return 'I Love ' + name;
};
// 换成
const Func = name => 'I Love ' + name;
一次性函数：适用于运行一些只需执行一次的初始化代码
function Func() {
console.log('x');
Func = function() {
console.log('y');
}
}
Func();
惰性载入函数：函数内判断分支较多较复杂时可大大节约资源开销
function Func() {
if (a === b) {
console.log('x');
} else {
console.log('y');
}
}
// 换成
function Func() {
if (a === b) {
Func = function() {
console.log('x');
}
} else {
Func = function() {
console.log('y');
}
}
return Func();
}
检测非空参数
function IsRequired() {
throw new Error('param is required');
}
function Func(name = IsRequired()) {
console.log('I Love ' + name);
}
Func(); // "param is required"
Func('You'); // "I Love You"
字符串创建函数
const Func = new Function('name', `console.log("I Love " + ${name})`);
优雅处理错误信息
try {
Func();
} catch (e) {
location.href = `https://stackoverflow.com/search?q=[js]+${e.message}`;
}
优雅处理Async/Await参数
async function AsyncTo(promise) {
return promise.then(data => [null, data]).catch(err => [err]);
}
const [err, res] = await AsyncTo(Func());
优雅处理多个函数返回值
async function Func() {
return Promise.all([
fetch('/user'),
fetch('/comment')
]);
}
const [user, comment] = await Func(); // 需在async包围下使用
显示全部DOM边框：调试页面元素边界时使用
[].forEach.call($$('*'), dom => {
dom.style.outline = '1px solid #' + (~~(Math.random() * (1 << 24))).toString(16);
});
自适应页面：页面基于一张设计图但需做多款机型自适应，元素尺寸使用rem进行设置
function AutoResponse(width = 750) {
const target = document.documentElement;
target.clientWidth >= 600
? (target.style.fontSize = '80px')
: (target.style.fontSize = target.clientWidth / width * 100 + 'px');
}
过滤XSS
function FilterXss(content) {
let elem = document.createElement('div');
elem.innerText = content;
const result = elem.innerHTML;
elem = null;
return result;
}
存取LocalStorage：反序列化取，序列化存
const love = JSON.parse(localStorage.getItem('love'));
localStorage.setItem('love', JSON.stringify('I Love You'));
银行卡号分割
bank_filter = val =>{
val += '';
val = val.replace(/(\s)/g,'').replace(/(\d{4})/g,'$1 ').replace(/\s*$/,'');
return val;
}
数字超过99显示99+
nineNumFilter = val =>{
val = val?val-0:0;
if (val > 99 ) {
return '99+'
}else{
return val;
}
}
防抖与节流
/**
* 函数防抖 (只执行最后一次点击)
*/
Debounce = (fn, t) => {
let delay = t || 500;
let timer;
return function () {
let args = arguments;
if(timer){
clearTimeout(timer);
}
timer = setTimeout(() => {
timer = null;
fn.apply(this, args);
}, delay);
}
};
/*
* 函数节流
*/
Throttle = (fn, t) => {
let last;
let timer;
let interval = t || 500;
return function () {
let args = arguments;
let now = +new Date();
if (last && now - last < interval) {
clearTimeout(timer);
timer = setTimeout(() => {
last = now;
fn.apply(this, args);
}, interval);
} else {
last = now;
fn.apply(this, args);
}
}
};