es6之iterator

{
    console.log("lesson3加载");
    //iterator 基本用法  iterrator在数组中本身就有
    let arr=["hello","word"];
    let map=arr[Symbol.iterator]();
    console.log("1",map.next());
    console.log("2",map.next());
    console.log("3",map.next());
}

{
    //自定义iterator
    let obj={
        start:[1,3,2],
        end:[7,8,9],
        [Symbol.iterator](){
            let self=this;
            let index=0;
            let arr=self.start.concat(self.end);
            let len=arr.length;
            return {
                next(){
                    if(index<len){
                        return {
                            value:arr[index++],
                            done:false
                        }
                    }else{
                        return {
                            value:arr[index++],
                            done:true
                        }
                    }
                }
            }
        }
    }

    for(let key of obj){
        console.log(key);
    }



}