Promise,async,await

1. 普通的Promise

     <script>
       function t1(resolve, reject) {
         return new Promise(function (resolve, reject) {
           setTimeout(() => {
             console.log('1s执行')
             resolve('code：200 1s')
           }, 1000)
         });
       }
       function t2(resolve, reject) {
         return new Promise(function (resolve, reject) {
           setTimeout(() => {
             console.log('2s执行')
             resolve('code：200 2s')
           }, 2000)
         });
       }
   
       var p = new Promise(function (resolve, reject) {
         console.log('开始');
         resolve(123);
       });
       p.then(t2)
         .then(t1)
         .then(res => {
           console.log(res)
         })
       //执行打印顺序
       //开始
       //2s执行
       //1s执行
       //code：200 1s

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2. Promise all

       Promise.all([t1(),t2()]).then(res=>{
         console.log(res)
       })
   

       //执行打印顺序

       //1s执行

       //2s执行

       //["code：200 1s", "code：200 2s"]

3. Promise race

       Promise.race([t1(),t2()]).then(res=>{
         console.log(res)
       }).catch(res=>{
         console.log('reject')
       })
       //执行打印顺序
       //1s执行
       //code：200 1s
       //2s执行

4. async+await 串行执行

     async function asyncAwaitFn(str) {
       return await new Promise((resolve, reject) => {
           setTimeout(() => {
               resolve(str)
           }, 1000);
       })
   }
   
   const test = async () => { //串行执行
       console.time('test')
       console.log(await asyncAwaitFn('执行1')); //执行1
       console.log(await asyncAwaitFn('执行1')); //执行2
       console.timeEnd('test') //test: 2004.552978515625ms
   }
   
   test();

5. async+await 并行执行

     async function asyncAwaitFn(str) {
       return await new Promise((resolve, reject) => {
           setTimeout(() => {
               resolve(str)
           }, 1000);
       })
   }
   
   const test = async () => { //并行执行
       console.time('test')
        const parallelOne = asyncAwaitFn('执行1');
        const parallelTwo = asyncAwaitFn('执行2')
   
        console.log(await parallelOne) //执行1
        console.log(await parallelTwo) //执行1
        console.timeEnd('test') //test: 1002.541015625ms
   }
   
   test();

原文地址：https://www.cnblogs.com/tiger4513/p/11882368.html