秒懂promise 与 async await

原文链接：https://www.cnblogs.com/zddzz/p/10831668.html

promise方法

    let p1 = new Promise((resolve,reject) => {
        setTimeout(() => {
            resolve('我是p1')
        },4000)
    })
    let p2 = new Promise((resolve,reject) => {
        setTimeout(() => {
            resolve('我是p2')
        },200)
    })
    let p3 = new Promise((resolve,reject) => {
        setTimeout(() => {
            resolve('我是p3')
        },200)
    })
    // 想让p1完成后再执行P2再执行P3
    // 数量太多只能循环嵌套
    p1.then((res) => {
        console.log(res);
        p2.then((res) => {
            console.log(res);
            p3.then((res) => {
                console.log(res);
            })
        })
    })

async await语法糖

 let a1=()=>{
     return new Promise((resolve,reject) => {
         setTimeout(() => {
             resolve('我是a1')
         },4000)
     })
 } 
 let a2=()=>{
     return new Promise((resolve,reject) => {
         setTimeout(() => {
             resolve('我是a2')
         },40)
     })
 } 
 let a3=()=>{
     return new Promise((resolve,reject) => {
         setTimeout(() => {
             resolve('我是a3')
         },40)
     })
 } 
 // 想让a1完成后再执行a2再执行a3
 //能避免回调
 async function asy(){
     await a1().then((res) => {console.log(res)});
     await a2().then((res) => {console.log(res)});
     await a3().then((res) => {console.log(res)});
 }
 asy();