Promise的面试题基本都是代码题，不提供参考答案，否则容易干扰思考

若需知道正确答案，请自行运行

1. 下面代码的输出结果是什么

   js

   const promise = new Promise((resolve, reject) => {
       console.log(1); 
       resolve(); 
       console.log(2);
   })
   
   promise.then(() => {
       console.log(3);
   })
   
   console.log(4);

2. 下面代码的输出结果是什么

   js

   const promise = new Promise((resolve, reject) => {
       console.log(1); 
       setTimeout(()=>{
         console.log(2)
         resolve(); 
       	console.log(3);
       })
   })
   
   promise.then(() => {
       console.log(4);
   })
   
   console.log(5);

3. 下面代码的输出结果是什么

   js

   const promise1 = new Promise((resolve, reject) => {
   	setTimeout(() => {
       resolve()
     }, 1000)
   })
   const promise2 = promise1.catch(() => {
     return 2;
   })
   
   console.log('promise1', promise1) 
   console.log('promise2', promise2) 
   
   setTimeout(() => {
     console.log('promise1', promise1) 
     console.log('promise2', promise2) 
   }, 2000)

4. 下面代码的输出结果是什么

   js

   async function m(){
     const n = await 1;
     console.log(n);
   }
   
   m();
   console.log(2);

5. 下面代码的输出结果是什么

   js

   async function m(){
     const n = await 1;
     console.log(n);
   }
   
   (async ()=>{
     await m();
     console.log(2);
   })();
   
   console.log(3);

6. 下面代码的输出结果是什么

   js

   async function m1(){
     return 1;
   }
   
   async function m2(){
     const n = await m1();
     console.log(n)
     return 2;
   }
   
   async function m3(){
     const n = m2();
     console.log(n);
     return 3;
   }
   
   m3().then(n=>{
     console.log(n);
   });
   
   m3();
   
   console.log(4);

7. 下面代码的输出结果是什么

   js

   Promise.resolve(1)	
     .then(2)
     .then(Promise.resolve(3))
     .then(console.log)

8. 下面代码的输出结果是什么

   js

   var a;
   var b = new Promise((resolve, reject) => {
     console.log('promise1');
     setTimeout(()=>{
       resolve();
     }, 1000);
   }).then(() => {
     console.log('promise2');
   }).then(() => {
     console.log('promise3');
   }).then(() => {
     console.log('promise4');
   });
   
   a = new Promise(async (resolve, reject) => {
     console.log(a);
     await b;
     console.log(a);
     console.log('after1');
     await a
     resolve(true);
     console.log('after2');
   });
   
   console.log('end');

9. 下面代码的输出结果是什么

   js

   async function async1() {
       console.log('async1 start');
       await async2();
       console.log('async1 end');
   }
   async function async2() {
   	console.log('async2');
   }
   
   console.log('script start');
   
   setTimeout(function() {
       console.log('setTimeout');
   }, 0)
   
   async1();
   
   new Promise(function(resolve) {
       console.log('promise1');
       resolve();
   }).then(function() {
       console.log('promise2');
   });
   console.log('script end');