generator 和 co模块

// 类数组的生成器
function fns() {
	let obj = {0:1,1:2,2:3,length: 3}, [Symbol.iterator]: function() {
		let index = 0;
		let that = this;
		return {
			next() {
				return {
					value: that[index],
					done: index++ === that.length
				}
			}
		}
	}
	let arr = [...obj];
	console.log(Array.isArray(arr), arr);
}

// 自动执行next
function fns() {
	// 给类数组添加迭代方法
	let obj = {0:1,1:2,2:3,length: 3}, [Symbol.iterator]: function() {
		let index = 0;
		let that = this;
		while(index === that.length) {
			yield that[index++]
		}
	}
	let arr = [...obj];
	console.log(Array.isArray(arr), arr);
}
fns(1,2,3,4,5)

// generator + promise 来使用
let fs = require(‘fs‘).promises;

// promise 要通过then  generator 可以省略then方法
function* read() {
    // try{
        let content = yield fs.readFile(‘./name.txt‘,‘utf8‘);
        let age = yield fs.readFile(content,‘utf8‘);
        let a = yield age + 100;
        return a;
    // }catch(err){
    //     console.log(err);
    // }
}
// co 库

function co(it){
    return new Promise((resolve,reject)=>{
        // 异步迭代 next
        function next(data){
           let {value,done} = it.next(data);
           if(!done){
               Promise.resolve(value).then(data=>{
                  next(data)
               },reject);
           }else{
                resolve(value);
           }
        }
        next();
    });
}
co(read()).then(data=>{
    console.log(data);
});