ES6的demo代码

ES6总结

扩展运算符

该文章是初次涉猎ES6做的笔记,刚开始简单的东西我就pass掉

代码运行环境(运行脚手架只需要在src/index.js写完代码输入npm run build就可以运行)

关于 ...的用法

let a=[1,2,3]
b=[...a]
b.push(6)
console(b) ==>1,2,3,6

关于rest运算符

function a(a,...arg)==>a(1,2,3),arg=[2,3]

字符串模板

字符串套变量

let a="china"
let b=`i am from ${a},<br>and you?`

判断是否包含字符串

let searchWorld="am"
let a="i am you"
//是否包含,开头是否包含,结尾是否包含
a.include(searchWorld)
a.startsWith(searchWorld)
a.endsWith(searchWorld)
//字符串自身复制,参数是次数,小数就取整
console.log(a.repeat(3))

数字判断与扩展

进制(切记不是字符串)

//0B开头是二进制标志
let a = 0B0011
//打印3
console.log(a)
//0o开头是八进制标志
let a = 0o0011
console.log(a)

Number对象方法

let a = 10/3
//判断是不是数字
console.log(Number.isFinite(a))//true
//判断是不是NaN
console.log(Number.isNaN(NaN))//true
//转换整数小数
console.log(Number.parseInt(a))//取整
console.log(Number.parseFloat(a))
//判断是否为整数
console.log(Number.isInteger(a))//false
//es6的最大安全值
console.log(Math.pow(2,53)-1)
//最大,最小常量数,相当于const定义变量
console.log(Number.MIN_SAFE_INTEGER)
console.log(Number.MAX_SAFE_INTEGER)
//判断是否安全数字
console.log(Number.isSafeInteger(a))//true

Math对象

trunc模块

//将字符串转为数字
console.log(Math.trunc("123"))//123
console.log(Math.trunc("12abc"))//NaN
console.log(Math.trunc("abc"))//NaN

sign模块

//判断正负数
console.log(Math.sign(-123))//-1
console.log(Math.sign(123))//1
console.log(Math.sign(0))//0

cbrt模块

//计算立方根
console.log(Math.cbrt(8))

clz32模块

//计算32位二进制
console.log(Math.clz32(8))

imul模块

//计算乘法
console.log(Math.imul(8))//0
console.log(Math.imul(8,2))//16

hydop

//计算乘法
console.log(Math.hypot(1,1,1,1))//return (1^2+1^2+1^2+1^2)的平方根==>2

在github传了官方pdf,更多方法就在那里查阅

数组实例与应用

from模块=>json转数组

let jsonData={
  "0":0,
  "1":1,
  "2":2,
  "length":3
}
let arr=Array.from(jsonData)
console.log(arr)//[0,1,2]

of模块=>文本转数组

let txt="1,2,3,4,5"
let data=Array.of(txt)
console.log(data)

copyWithin模块=>第一个是准备要替换位置,第二个是开始截取替换位置,第三个是最后截止位置,函数执行将截取的数据从起始位置开始覆盖

let arr=[0,1,2,3,4,5,6,7,8]
console.log(arr.copyWithin(1,3,8))//[0,3,4,5,6,7,6,7,8]

find模块=>依次遍历,遇到条件为true则返回

let arrDemo=[0,1,2,3,4,5,6,1,8]
console.log(arrDemo.find((value,index,arr)=>{
  return value >5
}))//6

fill模块=>遍历替代,第一个参数表示要替代的值,第二个是替代开始位置,第三个是替代终止位置

let arrDemo=[0,1,2,3,4,5,6,1,8]
console.log(arrDemo.fill("x",2,5))
//[0, 1, "x", "x", "x", 5, 6, 1, 8]

of模块=>遍历每个元素

let arrDemo=[0,1,2,3,4,5,6,1,8]
for (let i of arrDemo) {
  console.log(i)//依次打印每个元素
}

in模块与of一样

let arrDemo=[0,1,2,3,4,5,6,1,8]
for (let i in arrDemo) {
  console.log(i)
}

<span style="color:red;font-weight:bold">在有些场景in不好用,例如</span>

let arrDemo=["1","2","3"]
for (let [index,val] of arrDemo.entries()) {
  console.log(index,val)
}//能输出key和value

let arrDemo=["1","2","3"]
for (let [index,val] in arrDemo.entries()) {
  console.log(index,val)
}//不能输出

entries

let arrDemo=["a","b","c"]
let flag=arrDemo.entries()
console.log(flag.next().value)
console.log(flag.next().value)
console.log(flag.next().value)
console.log(flag.next().value)
//输出[0,"a"],[1,"b"],[2,"c"]

function模块

参数预设值 ==>不可以使用严谨模式

function addDemoOne(a,b){
  return a+b
}
function addDemoTwo(a,b=3){
  return a+b
}
console.log(addDemoOne(2,3))//5
console.log(addDemoTwo(2))//5

参数覆盖

function addDemoTwo(a,b=3){
  return a+b
}
console.log(addDemoTwo(1,2))//3

预设函数违法值

function addDemoTwo(a,b=3){
  if(a === 1){
    throw new Error("值错误")
  }
  return a+b
}
console.log(addDemoTwo(1))//Uncaught Error: 值错误

计算函数几个参数

在这里有个坑,请看demo2,3

function addDemoOne(a,b,c){
  return a+b
}
console.log(addDemoOne.length)//3
function addDemoTwo(a,b,c=2){
  return a+b
}
console.log(addDemoTwo.length)//2
function addDemoThree(a,b=2,c){
  return a+b
}
console.log(addDemoThree.length)//1

function的name模块

function addDemoOne(a,b,c){
  return a+b
}
console.log(addDemoOne.name)//addDemoOne
let addDemoTwo = function addDemoThree(){}
console.log(addDemoTwo.name)//addDemoThree

箭头函数

let demo = (a,b) => a+b//省略 return,如果加return则必须加{}
console.log(demo(2,3))//5

解构对象

let jsonData={
  a:100,
  b:200
}
function addDemoTwo({a,b=3}){
  return a+b
}
console.log(addDemoTwo(jsonData))//300

判断json存在某属性

let jsonData={
    a:1,
    b:2
}
console.log("a" in jsonData)//true
console.log("c" in jsonData)//false

判断数组是否为空

let arrOne=[,,,,]
let arrTwo=[1,2,3]
console.log(0 in arrOne)//false
console.log(0 in arrTwo)//true

将对象合并

var a={a:1}
var b={b:2}
var c=Object.assign(a,b)//可以合并多个
console.log(c)//{a: 1, b: 2}

解构数组

let arr =[1,2,3,4]
function addDemoTwo(a,b,c,d){
  console.log(a,b,c,d)
}
addDemoTwo(...arr)//1,2,3,4

Symbol类型=>独一无二的类型

let testData=Symbol('hello')
console.log(testData)//Symbol(hello)
console.log(typeof testData)//symbol

symbol的应用

let demoOne=Symbol('hello')
let demoTwo=Symbol('word')
let jsonData={
  a:'aaa',
  b:'bbb'
}
jsonData[demoOne]='ccc'
jsonData[demoTwo]='ddd'
for(let i in jsonData){
  console.log(jsonData[i])//遍历不出symbol属性
}
console.log(jsonData);//可以遍历出

Set与WeakSet=>数据集合

let demoData=new Set([1,2,3,4,5,5])//不允许重复元素
console.log(demoData);
demoData.add(6)
console.log(demoData);
demoData.delete(1)
console.log(demoData);
console.log(demoData.has(1));
console.log(demoData.has(2));
for (let i of demoData){
  console.log(i);
}
demoData.clear()
console.log(demoData);

去除数组中重复的元素可以这样

let arr=[1,2,3,3,4]
let setOne=new Set(arr)
console.log(setOne);

Weakset

let demo={a:1,b:2}
let setData=new WeakSet()
setData.add(demo)
console.log(setData);

Map

let json={name:"fan",age:18}
let m = new Map()
m.set(json,'me')
m.set('name','fan')
console.log(m.get('name'));//fan
console.log(m.get(json));//me,根据对象搜索

Proxy

Proxy本质是一个对象,当对对象的属性进行操作可以触发一系列操作

let data2=new Proxy({
  add:function(val){
    return val+1
  },
  name:'tom'
},{
  get:function(target,key,property){
    console.log('get key--->',key)//name
    console.log('get target--->',target);//obj
    console.log('get property--->',property);//proxy obj
    return target[key]
  },
  set:function(target,key,value,receiver){
    console.log('set key--->',key);//name
    console.log('set value--->',value);//3333
    console.log('set target--->',target);//obj
    console.log('set reeiver--->',receiver);//proxy obj
    return target[key]=value
  }
})
data2.name=3333//执行set
console.log(data2.name);//执行get

apply--->执行的时候必须调用

let target = ()=>{
  return 'hello world'
}
let handler = {
  apply(target,ctx,args){
    //不要加钩子
    console.log('6666');
    return Reflect.apply(...arguments)//Reflect代码demo本身
  }
}
let demo=new Proxy(target,handler)
demo()//6666

Promise

promise就是前一步完成了动作就执行下一步操作

let flag=200
function one(resolve,reject){
  console.log("one");
  if(flag==200){
    resolve("step1 finish")
  }else{
    reject("step1 erro")
  }
}
function two(resolve,reject){
  console.log("two");
  if(flag==200){
    resolve("step2 finish")
  }else{
    reject("step2 erro")
  }
}
function three(resolve,reject){
  console.log("three");
  if(flag==200){
    resolve("step3 finish")
  }else{
    reject("step3 erro")
  }
}

new Promise(one).then(function(val){
  console.log(val);
  return new Promise(two)
}).then(function(val){
  console.log(val);
  return new Promise(three)
}).then(function(val){
  console.log(val);
  return val
})

Class语法糖

class people{
  name(val){
    // console.log(val);
    return val
  }
  fullname(val){
    console.log('Mr'+this.name(val))
  }
  add(){
    return this.x+this.y
  }
  constructor(x,y){
    this.x = x
    this.y = y
  }
}
let p = new people(1,2)
console.log(p.add());
class student extends people{
  hello(){
    console.log("hello");
  }
}
let s= new student(10,20)
console.log(s.add());