ES6的demo代码

摘要：总结扩展运算符该文章是初次涉猎做的笔记刚开始简单的东西我就掉代码运行环境运行脚手架只需要在写完代码输入就可以运行关于的用法关于运算符字符串模板字符串套变量判断是否包含字符串是否包含开头是否包含结尾是否包含字符串自身复制参数是次数小数就取整数

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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

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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)

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

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

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

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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))

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//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)

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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

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//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

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

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//计算立方根
console.log(Math.cbrt(8))

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//计算32位二进制
console.log(Math.clz32(8))

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

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//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

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在github传了官方pdf,更多方法就在那里查阅

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

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

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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]

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

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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]

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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
}

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

在有些场景in不好用,例如

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

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

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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"]

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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

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

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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

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在这里有个坑,请看demo2,3

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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

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

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

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

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判断json存在某属性

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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

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

将对象合并

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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}

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

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

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

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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);

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去除数组中重复的元素可以这样

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

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

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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

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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

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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

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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

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promise就是前一步完成了动作就执行下一步操作

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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
})

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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());