2021高频实用的 JavaScript 片段

let someThingTrue = true
if(someThingTrue){
    handleTrue()
}else{
    handleFalse()
}

****** 以下是简短版本 ******

let someThingTrue = true
someThingTrue ?  handleTrue() : handleFalse()复制代码

const defaultValue = "SomeDefaultValue"
let someValueNotSureOfItsExistance = null
let expectingSomeValue = someValueNotSureOfItsExistance ||     defaultValue

console.log(expectingSomeValue) // SomeDefaultValue复制代码

let someValue = true
if (someValue) {
  console.log('条件成立!')
}复制代码

for (let i = 0; i < 1e2; i++) { // 代替 i<100 是不是有点酷
}复制代码

let someValues = [1, 2, 4]
for (let val in someValues) {
  console.log(val)
}
let obj = {
  'key1': 'value1',
  'key2': 'value2',
  'key3': 'value3'
}
for (let key in obj) {
  console.log(key)
}复制代码

let x='x',y='y'
let obj = {x,y}

console.log(obj) // {x: "x", y: "y"}复制代码

const credits = {
  producer: '大迁世界',
  name: '前端小智',
  rating: 9
}
const arr = Object.entries(credits)
console.log(arr)

*** 输出 ***
[ [ 'producer', '大迁世界' ], [ 'name', '前端小智' ], [ 'rating', 9 ] ]复制代码

const credits = {
  producer: '大迁世界',
  name: '前端小智',
  rating: 9
}
const arr = Object.values(credits)
console.log(arr)

*** 输出 ***

[ '大迁世界', '前端小智', 9 ]复制代码

let name = '前端小智'
let age = 20
var someStringConcatenateSomeVariable = `我是 ${name}，今年 ${age} 岁`
console.log(someStringConcatenateSomeVariable)复制代码

import { observable, action, runInAction } from 'mobx';复制代码

let multiLineString = `some string\n
with multi-line of\n
characters\n`

console.log(multiLineString)复制代码

const pets = [{
    type: 'Dog',
    name: 'Max'
  },
  {
    type: 'Cat',
    name: 'Karl'
  },
  {
    type: 'Dog',
    name: 'Tommy'
  }
]
pet = pets.find(pet => pet.type === 'Dog' && pet.name === 'Tommy')

console.log(pet) // { type: 'Dog', name: 'Tommy' }复制代码

function area(h, w) {
  if (!h) {
    h = 1;
  }
  if (!w) {
    w = 1;
  }
  return h * w
}复制代码

function area(h = 1, w = 1) {
  return h * w
}复制代码

let sayHello = (name) => {
  return `你好，${name}`
}

console.log(sayHello('前端小智'))复制代码

let sayHello = name => `你好，${name}`

console.log(sayHello('前端小智'))复制代码

let someFuncThatReturnSomeValue = (value) => {
  return value + value
}
console.log(
someFuncThatReturnSomeValue('前端小智'))复制代码

let someFuncThatReturnSomeValue = (value) => (
  value + value
)
console.log(someFuncThatReturnSomeValue('前端小智'))复制代码

function mustHavePatamMethod(param) {
  if (param === undefined) {
    throw new Error('Hey You must Put some param!');
  }
  return param;
}复制代码

mustHaveCheck = () => {
  throw new Error('Missing parameter!')
}
methodShoudHaveParam = (param = mustHaveCheck()) => {
  return param
}复制代码

'SampleString'.charAt(0) // S
// 简写
'SampleString'[0]复制代码

function fn1() {
  console.log('I am Function 1')
}

function fn2() {
  console.log('I am Function 2')
}
/*
长的写法
*/
let checkValue = 3;
if (checkValue === 3) {
  fn1()
} else {
  fn2()
}复制代码

(checkValue === 3 ? fn1 : fn2)()复制代码

let val = '123.95'

console.log(Math.floor(val)) // 常规写法
console.log(~~val) // 简写复制代码

Math.pow(2, 3) // 8
// 简写
2 ** 3 // 8复制代码

const num1 = parseInt('100')
// 简写
console.log(+"100")
console.log(+"100.2")复制代码

let value = 1;
if (value === 1)
  console.log('Value is one')
//OR In short 
value && console.log('Value is one')复制代码

let someNumber = 123
console.log(someNumber.toString()) // "123"
// 简写
console.log(`${someNumber}`) // "123"复制代码