ES6的demo代碼

ES6總結

擴展運算符

該文章是初次涉獵ES6作的筆記,剛開始簡單的東西我就pass掉

代碼運行環境(運行腳手架只須要在src/index.js寫完代碼輸入npm run build就能夠運行)

關於 ...的用法

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

關於rest運算符

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

字符串模板

字符串套變量

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

判斷是否包含字符串

let searchWorld="am"
let a="i am you"
//是否包含,開頭是否包含,結尾是否包含
a.include(searchWorld)
a.startsWith(searchWorld)
a.endsWith(searchWorld)
//字符串自身複製,參數是次數,小數就取整
console.log(a.repeat(3))

數字判斷與擴展

進制(切記不是字符串)

//0B開頭是二進制標誌
let a = 0B0011
//打印3
console.log(a)
//0o開頭是八進制標誌
let a = 0o0011
console.log(a)

Number對象方法

let a = 10/3
//判斷是否是數字
console.log(Number.isFinite(a))//true
//判斷是否是NaN
console.log(Number.isNaN(NaN))//true
//轉換整數小數
console.log(Number.parseInt(a))//取整
console.log(Number.parseFloat(a))
//判斷是否爲整數
console.log(Number.isInteger(a))//false
//es6的最大安全值
console.log(Math.pow(2,53)-1)
//最大,最小常量數,至關於const定義變量
console.log(Number.MIN_SAFE_INTEGER)
console.log(Number.MAX_SAFE_INTEGER)
//判斷是否安全數字
console.log(Number.isSafeInteger(a))//true

Math對象

trunc模塊

//將字符串轉爲數字
console.log(Math.trunc("123"))//123
console.log(Math.trunc("12abc"))//NaN
console.log(Math.trunc("abc"))//NaN

sign模塊

//判斷正負數
console.log(Math.sign(-123))//-1
console.log(Math.sign(123))//1
console.log(Math.sign(0))//0

cbrt模塊

//計算立方根
console.log(Math.cbrt(8))

clz32模塊

//計算32位二進制
console.log(Math.clz32(8))

imul模塊

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

hydop

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

在github傳了官方pdf,更多方法就在那裏查閱

數組實例與應用

from模塊=>json轉數組

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

of模塊=>文本轉數組

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

copyWithin模塊=>第一個是準備要替換位置,第二個是開始截取替換位置,第三個是最後截止位置,函數執行將截取的數據從起始位置開始覆蓋

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模塊=>依次遍歷,遇到條件爲true則返回

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

fill模塊=>遍歷替代,第一個參數表示要替代的值,第二個是替代開始位置,第三個是替代終止位置

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模塊=>遍歷每一個元素

let arrDemo=[0,1,2,3,4,5,6,1,8]
for (let i of arrDemo) {
  console.log(i)//依次打印每一個元素
}

in模塊與of同樣

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">在有些場景in很差用,例如</span>

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

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

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)
//輸出[0,"a"],[1,"b"],[2,"c"]

function模塊

參數預設值 ==>不能夠使用嚴謹模式

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

參數覆蓋

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

預設函數違法值

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

計算函數幾個參數

在這裏有個坑,請看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模塊

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

箭頭函數

let demo = (a,b) => a+b//省略 return,若是加return則必須加{}
console.log(demo(2,3))//5

解構對象

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

判斷json存在某屬性

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

判斷數組是否爲空

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

將對象合併

var a={a:1}
var b={b:2}
var c=Object.assign(a,b)//能夠合併多個
console.log(c)//{a: 1, b: 2}

解構數組

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類型=>獨一無二的類型

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

symbol的應用

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])//遍歷不出symbol屬性
}
console.log(jsonData);//能夠遍歷出

Set與WeakSet=>數據集合

let demoData=new Set([1,2,3,4,5,5])//不容許重複元素
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);

去除數組中重複的元素能夠這樣

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,根據對象搜索

Proxy

Proxy本質是一個對象,當對對象的屬性進行操做能夠觸發一系列操做

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//執行set
console.log(data2.name);//執行get

apply--->執行的時候必須調用

let target = ()=>{
  return 'hello world'
}
let handler = {
  apply(target,ctx,args){
    //不要加鉤子
    console.log('6666');
    return Reflect.apply(...arguments)//Reflect代碼demo自己
  }
}
let demo=new Proxy(target,handler)
demo()//6666

Promise

promise就是前一步完成了動做就執行下一步操做

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語法糖

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());