每次操作dom都會導(dǎo)致
頁面重繪，重新渲染
數(shù)據(jù)類型
Number String Boolean Null Udefined
Object function
symbol
pop shift unshif push splice reverse sort
indexOf lastIndexOf
concat slice

forEach filter map filter some every reduce
find includes

let arr=[1,2,3]
arr.b=100
for(let i=0;i<arr.length;i++){
      console.log(arr[i])
}
arr.map((item)=>{
  console.log(item)
})
for(let key in arr){
    console.log(typeof key)
    console.log(key)
}
for(let value of arr){
    console.log(value)
}

let obj={
  name:'jh',
  age:15
}
for(let key in obj){
    console.log(`${key} : ${obj[key]}`)
}
for(let value of Object.values(obj)){
    console.log(value)
}