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Promise to solve hell function calls can be used infinitely

2022-06-12 19:29:00 【laoli815】

js promise The returned result is still promise As long as you want to keep adjusting 

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <script src="https://cdn.bootcdn.net/ajax/libs/es6-promise/4.2.8/es6-promise.auto.js"></script>
</head>
<body>
<script> let l1=[1,2,3,4] console.log(l1[2]) const p=new Promise((resolve,reject)=>{
       reject(" Rejected brother, next time try ") }) const p2=new Promise((resolve,reject)=>{
       resolve(" I succeeded in ") }) Promise.all([p,p2]).then(res=>{
       console.log("p,p2 All have been carried out ") }).catch(err=>{
       console.log("p,p2 One failed to execute ",err) }) console.log(p) console.dir(p) const t=p.then(res=>{
       console.log(res," I love Beijing Tian'an incisors ") }).catch(rej=>{
       console.log(" The rejected content is ",rej) }) .then(res=>{
       console.log(" Xiao Ming is a good boy ") }).then(res=>{
       console.log(" Wang Dana's country love is beautiful. I like it ") return Promise.reject(" Is to refuse you ") }) console.log(t) console.dir(t) f=t.then(res=>{
       console.log(" Well, yes, it was rejected ") }).catch(err=>{
       console.log(err," The boy was rejected ") }) console.log(f) console.dir(f) f.then(res=>{
       console.log(" I am so sad that I have been lovelorn ") }).catch(err=>{
       console.log(" Xiao Ming likes to go to the gym ") }).then(res=>{
       console.log(" Just like you ") }) </script>
</body>
</html>

Execution results
Insert picture description here

promise.then and catch All the returned values of are promise, With or without return It can be accessed continuously , But it should be noted that only when promise The state of is rejected It will call catch Of course, if promise If there is an error code in the execution body, it will also execute , When the state is fulfilled It will call then, therefore catch If the statement is executed correctly , Still call then Method

But there's a question console.log(t) console.dir(t) Why do you put it in front of you and execute it in advance , state pending I can still understand , however fulfilled Why not , You can tell me what you know in the comment area. Thank you

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本文为[laoli815]所创，转载请带上原文链接，感谢
https://yzsam.com/2022/02/202202281546449207.html

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