Iterator

已经部署Iterator接口的数据
array、map、set、string、TypeArray、NodeList、arguments

obj添加遍历起

    let obj={
        a:1,
        b:2,
        c:3,
        [Symbol.iterator](){
            let nextIndex=0;
            let map=new Map();
            for(let [key,value] of Object.entries(this)) {
                map.set(key,value)
            }
            let mapEnteries=[...map.entries()];
            return {
                next(){
                    return nextIndex<mapEnteries.length?
                    {value: mapEnteries[nextIndex++],done: false}:{
                        value: undefined,done: true
                    }
                }
            }
        }
    }
    for(let i of obj){
        console.log(i)
    }
使用generator函数
let obj={
  a:0,
  b:9,
  [Symbol.iterator]: function *(){
        let nextIndex=0;
            let map=new Map();
            for(let [key,value] of Object.entries(this)) {
                map.set(key,value)
            }
            let mapEnteries=[...map.entries()];
                    while(nextIndex<len){
              yield arr[nextIndex++]
            }
  }
}

Generator

generator也是迭代器可以用for…of遍历

function * foo(){
  let value1=yield 1;
  console.log(value1); //two
  let value2=yield 2;
  let value3=yield 3;
}
let iter=foo();
iter.next('one')
iter.next('two')

let fs=require('fs');
fs.readFile('./name.txt','utf-8',(err,data)=>{
    fs.readFile(data,'utf-8',(err,data)=>{
        fs.readFile(data,'utf-8',(err,data)=>{
            console.log(data)
        })
    })
})
function promisify(fn) {
    return function(...args) {
        return new Promise((resolve,reject)=>{
            fn(...args,(err,data)=>{
                if(err){
                    reject(err);
                }else{
                    resolve(data)
                }
            })
        })
    }
}
let readFile=promisify(fs.readFile);
readFile('./name.txt','uft-8')
.then(res=>readFile(res,'utf-8'))
.then(res=>readFile(res,'utf-8'))
.then(res=>console.log(res))
function * read() {
    let value1=yield readFile('./name.txt','utf-8');
    let value2=yield readFile(value1,'utf-8');
    let value3=yield readFile(value2,'utf-8');
    console.log(value3)
}
let iter=read();
let {value,done}=iter.next();
value.then((val1)=>{
    let {value,done}=iter.next(val1);
    value.then((val2)=>{
        let {value,done}=iter.next(val2);
        value.then((val3)=>{
            console.log('val3',val3)
        })
    })
})
优化：
function Co(iter) {
   return new Promise((resolve,reject)=>{
     let next=(data)=>{
       let {value,done}=iter.next(data);
       if(done) {
         resolve(value);
       }else{
         value.then((val)=>{
           next(val)
         })
       }
       next();
     }
   })
}
let promise=Co(read());
promise.then((val)=>{
  console.log(val);
})