189 lines
3.1 KiB
Markdown
189 lines
3.1 KiB
Markdown
> 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
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>
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> 若需知道正确答案，请自行运行
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1. 下面代码的输出结果是什么
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```js
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const promise = new Promise((resolve, reject) => {
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console.log(1);
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resolve();
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console.log(2);
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})
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promise.then(() => {
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console.log(3);
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})
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console.log(4);
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```
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2. 下面代码的输出结果是什么
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```js
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const promise = new Promise((resolve, reject) => {
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console.log(1);
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setTimeout(()=>{
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console.log(2)
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resolve();
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console.log(3);
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})
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})
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promise.then(() => {
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console.log(4);
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})
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console.log(5);
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```
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3. 下面代码的输出结果是什么
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```js
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const promise1 = new Promise((resolve, reject) => {
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setTimeout(() => {
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resolve()
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}, 1000)
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})
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const promise2 = promise1.catch(() => {
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return 2;
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})
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console.log('promise1', promise1)
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console.log('promise2', promise2)
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setTimeout(() => {
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console.log('promise1', promise1)
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console.log('promise2', promise2)
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}, 2000)
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```
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4. 下面代码的输出结果是什么
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```js
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async function m(){
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const n = await 1;
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console.log(n);
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}
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m();
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console.log(2);
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```
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5. 下面代码的输出结果是什么
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```js
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async function m(){
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const n = await 1;
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console.log(n);
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}
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(async ()=>{
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await m();
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console.log(2);
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})();
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console.log(3);
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```
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6. 下面代码的输出结果是什么
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```js
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async function m1(){
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return 1;
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}
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async function m2(){
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const n = await m1();
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console.log(n)
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return 2;
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}
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async function m3(){
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const n = m2();
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console.log(n);
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return 3;
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}
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m3().then(n=>{
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console.log(n);
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});
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m3();
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console.log(4);
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```
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7. 下面代码的输出结果是什么
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```js
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Promise.resolve(1)
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.then(2)
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.then(Promise.resolve(3))
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.then(console.log)
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```
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8. 下面代码的输出结果是什么
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```js
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var a;
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var b = new Promise((resolve, reject) => {
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console.log('promise1');
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setTimeout(()=>{
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resolve();
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}, 1000);
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}).then(() => {
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console.log('promise2');
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}).then(() => {
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console.log('promise3');
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}).then(() => {
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console.log('promise4');
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});
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a = new Promise(async (resolve, reject) => {
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console.log(a);
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await b;
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console.log(a);
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console.log('after1');
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await a
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resolve(true);
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console.log('after2');
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});
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console.log('end');
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```
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9. 下面代码的输出结果是什么
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```js
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async function async1() {
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console.log('async1 start');
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await async2();
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console.log('async1 end');
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}
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async function async2() {
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console.log('async2');
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}
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console.log('script start');
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setTimeout(function() {
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console.log('setTimeout');
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}, 0)
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async1();
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new Promise(function(resolve) {
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console.log('promise1');
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resolve();
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}).then(function() {
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console.log('promise2');
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});
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console.log('script end');
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```
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