7-3 数组扩展：Array.prototype.flat()，Array.prototype.flatMap()

7-3 数组扩展：Array.prototype.flat()，Array.prototype.flatMap()

类数组/ 伪数组 Array.from() Array.of() copyWithin() fill() includes()

const divs = document.getElementsByTagName('div')
console.log(divs) // HTMLCollection

const divs2 = document.getElementsByClassName('xx')
console.log(divs2) // HTMLCollection

const divs3 = document.querySelectAll('.xx')
console.log(divs3 instanceof Array) // NodeList
divs3.push(123)

let arr = Array.prototype.slice.call(div3)
console.log(arr)
arr.push(123)
console.log(arr)

function foo(){
  console.log(arguments instanceof Array)
}
foo(1, 'uu', true)

let arrayLike = {
  0:'es6',
  1:'es7',
  2:'es8',
  length:3
}
let arr = Array.from(arrayLike)
arr.push('es9')
console.log(arr)