ES6 Iterator 和 for..of vs for...in

Iterator迭代器(便利器)

提高访问具有遍历借口数据的效率

相当于指针(默认是-1)；

可便利借口

有next方法(next将当前指针移动到下个位置，返回一个对象{value:,done:})

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);

自定义便利器

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}

for..of vs for...in

普通循环便利

var arr=[1,2,3,4,5,6];
for (var i = 0, l = arr.length; i<l; i++) {
console.log(arr[i]);
};
arr.forEach(i=>{
console.log(i);
})

迭代器便利

var bb=arrSymbol.iterator;
var cc=bb.next();
while(!cc.done){
console.log(cc.value);
cc=bb.next();
}

for of array 便利

for(var item of arr){
console.log(item);
}

for of set 便利

var s=new Set(['a','b','c']);
for(var item of s){
console.log(item);
}

for in 用来便利对象

//
var obj={
x:1,y:2,z:3
}
for(var i in obj ){
console.log(i)//x,y,z
console.log(obj[i]);//x 1 y 2 z 3
}