如何判断Array类型以及Array.from()和[...]的

//如果判断Array类型
var arr = [];
arr instanceof Array; //true
Array.isArray(arr); //true
Object.prototype.toString.call(arr).slice(8,-1); //"Array"

Array.from 和 [...] 都可以将类数组转为数组
Array.from 只要有索引和长度
[...]则必须可以被迭代

var obj = { 0: 1, 1: 2, 2: 3, length: 3 };
Array.from(obj); //[1,2,3]
[...obj]; //Uncaught TypeError: object is not iterable (cannot read property Symbol(Symbol.iterator))


var obj = {
  0: 1,
  1: 2,
  2: 3,
  length: 3,
  [Symbol.iterator]: function* () {
    var index = 0;
    while (index < this.length) {
      yield this[index++];
    }
  },
};
Array.from(obj); //[1,2,3]
[...obj]; //[1,2,3]