Iterator

数组默认有迭代器属性

var arr = [111,222,333];
var aa = arrSymbol.iterator;
aa.next(); // { value: 111, done: false }
aa.next(); // { value: 222, done: false }
aa.next(); // { value: 333, done: false }
aa.next(); // { value: undefined, done: true }

可以用在 数组 Map Set 类数组

var m = new Set([11,22,33]);//set类似于数组
console.log(m);
var qq=mSymbol.iterator;
console.log(qq.next());//{value: 11, done: false}

var s = new Map([['name','shi'],['age',3]]);
s.set("sex",'nv')
console.log(s);
var i=sSymbol.iterator;
console.log(i.next());

类数组

var try=document.getElementsByName("div");
console.log(try);

自定义遍历器

var arr = [111,222,333];
function aa(arr){
var i=-1;
function next(){
i++;
let value;
let done=false;

if (i==arr.length) {
value=undefined;
done=true;
}else{
value=arr[i];
}
return{value:value,done:done};
}
return {next:next};
}

var zz=aa(arr);
console.log(zz.next());//Object {value: 111, done: false}
console.log(zz.next());//Object {value: 222, done: false}
console.log(zz.next());//Object {value: 333, done: false}
console.log(zz.next());//Object {value: undefined, done: true}