array/数值拓展、ArrayOf、ArrayFrom

let obj = {
    start: [1, 2, 3, 4, 5,],
    end: [6, 7],
    [Symbol.iterator]() {
        let idx = 0,
            arr = [...this.start, ...this.end],
            len = arr.length;
        return {
            next() {
                return idx < len ?
                    {
                        value: arr[idx++],
                        done:false,
                    }
                    :
                    {
                        value: undefined,
                        done: true,
                    }
            }
        }
    }
}
for (let i in obj) {
    console.log(i);
}
let arr = [1, 2, 3, 4, 5];
var iter = obj[Symbol.iterator]();
// ...拓展运算符 一定是该对象中存在Symbol.iterator属性
// 数组声明方式 
// console.log(new Array()) []
// console.log(new Array(3,1)) [3,1]
// console.log(Array.of(3)); [3]
// console.log(Array.of(3,4,6)); [3,4,6]
// Array.from(likeArray,mapFn,thisArg); 可以将类数组转成数组
// [].slice.call(likeArray);
var oList = document.querySelectorAll('p');
console.log([].slice.call(oList));
console.log(Array.from(oList));
console.log(Array.from(obj));
Array.from(oList, (item, idx) => {
    console.log()
    console.log(item);
    console.log(this.a);// undefined 箭头函数没有this
}, { a: 1 })
//  fill|,copyWith,|keys,values,entries|, |includes,find,findIndex|
// fill(val,startIdx(0),endIndx(数组长度))
var arr = [1, 2, 3, 4, 5];
arr.fill(5,)