blocks|key|3957992|text|您可以通过使用浏览器开发工具的控制台以及设置断点(如果您使用的是Chrome或Firefox，本文可能会有所帮助)来了解幕后发生的事情：|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|3957993|​|3957994|📷|atomic|3957995|3957996|正如您所看到的，您的所有10个承诺都是在执行其中任何一个之前创建的(解析/拒绝)。|3957997|有趣的是，在您的代码中，首先处理已解析的承诺。|3957998|如果在两个单独的定义中定义处理程序，您将获得预期的结果：|3957999|p.then((message)+=>+{
++++++++console.log(message)
++++})
p.catch((message)+=>+{
++++++++console.log(message)
++++})|code-block|syntax|javascript|3958000|输出：|3958001|3958002|3958003|3958004|entityMap|0|LINK|mutability|MUTABLE|url|https://developers.google.com/web/tools/chrome-devtools/javascript/|1|https://developer.mozilla.org/en-US/docs/Tools/Debugger|2|IMAGE|IMMUTABLE|imageUrl|https://ask.qcloudimg.com/http-save/yehe-900000/d6ff01da73f7e6de8bf84db08facfc5b.png|imageAlt|3|https://ask.qcloudimg.com/http-save/yehe-900000/6915f3aaea6ac4f1f66b64fdfdc34aa5.png^0|W|6|0|13|7|1|0|0|0|1|2|0|0|0|0|0|0|0|0|0|1|3|0|0^^$0|@$1|2|3|4|5|6|7|1H|8|@]|9|@$A|1I|B|1J|1|1K]|$A|1L|B|1M|1|1N]]|C|$]]|$1|D|3|E|5|6|7|1O|8|@]|9|@]|C|$]]|$1|F|3|G|5|H|7|1P|8|@]|9|@$A|1Q|B|1R|1|1S]]|C|$]]|$1|I|3|E|5|6|7|1T|8|@]|9|@]|C|$]]|$1|J|3|K|5|6|7|1U|8|@]|9|@]|C|$]]|$1|L|3|M|5|6|7|1V|8|@]|9|@]|C|$]]|$1|N|3|O|5|6|7|1W|8|@]|9|@]|C|$]]|$1|P|3|Q|5|R|7|1X|8|@]|9|@]|C|$S|T]]|$1|U|3|V|5|6|7|1Y|8|@]|9|@]|C|$]]|$1|W|3|E|5|6|7|1Z|8|@]|9|@]|C|$]]|$1|X|3|G|5|H|7|20|8|@]|9|@$A|21|B|22|1|23]]|C|$]]|$1|Y|3|E|5|6|7|24|8|@]|9|@]|C|$]]|$1|Z|3|-4|5|6|7|25|8|@]|9|@]|C|$]]]|10|$11|$5|12|13|14|C|$15|16]]|17|$5|12|13|14|C|$15|18]]|19|$5|1A|13|1B|C|$1C|1D|1E|-4]]|1F|$5|1A|13|1B|C|$1C|1G|1E|-4]]]]

You can see what's going on under the hood by using your the console of your browser's dev tools and, possibly, setting break points (this articles might be helpful if u're using <a href="https://developers.google.com/web/tools/chrome-devtools/javascript/" rel="nofollow noreferrer">Chrome</a> or <a href="https://developer.mozilla.org/en-US/docs/Tools/Debugger" rel="nofollow noreferrer">Firefox</a>):

<a href="https://i.stack.imgur.com/fnoZk.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/fnoZk.png" alt="enter image description here"></a>

As you can see, all your 10 promises are created before any of them are executed (resolve/reject).

Interestingly, in your code the resolved promises are handled first.

If you define the handlers in two separate definitions, you'll get the expected results:

<pre><code>p.then((message) =&gt; {
 console.log(message)
 })
p.catch((message) =&gt; {
 console.log(message)
 })
</code></pre>

Output:

<a href="https://i.stack.imgur.com/seFon.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/seFon.png" alt="enter image description here"></a>

blocks|key|3962116|text|重点是，promise是作为异步调用使用的，所以当您执行循环并为每次迭代创建一个新promise时，您正在创建新的实例，并且每个实例都可以在各自的时间内执行。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3962117|但这到底意味着什么呢？解释是，当你在一个循环中创建10个新的承诺时，每个承诺都会在他自己的时间内执行，并且很可能会打乱你的承诺解析顺序。|3962118|你能做些什么来解决这个问题？您可以使用await命令等待每个承诺的求解，如下面的代码所示：|offset|length|style|CODE|3962119|for+(let+i+=+0;+i+<+10;+i%2B%2B)+{
++++let+p+=+new+Promise((resolve,+reject)+=>+{

++++++++let+a+=+1+%2B+(i+%25+2)

++++++++if+(a+===+2)+{
++++++++++++resolve(i+%2B+'+resolve+'+%2B+a)
++++++++}+else+{
++++++++++++reject(i+%2B+'+reject+'+%2B+a)
++++++++}+++++++
++++})

++++await+p.then((message)+=>+{
++++++++console.log(message)
++++}).catch((message)+=>+{
++++++++console.log(message)
++++})
}|code-block|syntax|javascript|3962120|或者您可以尝试使用Promise.all()，它基本上可以为您解决订单问题，请参阅官方docs+here|3962121|entityMap|0|LINK|mutability|MUTABLE|url|https://developer.mozilla.org/fr/docs/Web/JavaScript/Reference/Objets_globaux/Promise/all^0|0|0|J|5|0|0|9|D|17|9|0|0^^$0|@$1|2|3|4|5|6|7|Y|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|Z|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|10|8|@$F|11|G|12|H|I]]|9|@]|A|$]]|$1|J|3|K|5|L|7|13|8|@]|9|@]|A|$M|N]]|$1|O|3|P|5|6|7|14|8|@$F|15|G|16|H|I]]|9|@$F|17|G|18|1|19]]|A|$]]|$1|Q|3|-4|5|6|7|1A|8|@]|9|@]|A|$]]]|R|$S|$5|T|U|V|A|$W|X]]]]

The point is, Promises are made to be used as Asynchronous calls, so when you execute your loop and for each iteration you creates a new promise, you are creating new instances, and each one of those can be executed in their own time.

But what this even means? The explanation is, when you create 10 new Promises in a loop, each promise will be executed in his own time and probablly will mess up with your promise solving order.

What you can do to solve it? You can use <code>await</code> command to wait each promise to solve, like the code bellow:

<pre><code>for (let i = 0; i &lt; 10; i++) {
 let p = new Promise((resolve, reject) =&gt; {

 let a = 1 + (i % 2)

 if (a === 2) {
 resolve(i + ' resolve ' + a)
 } else {
 reject(i + ' reject ' + a)
 } 
 })

 await p.then((message) =&gt; {
 console.log(message)
 }).catch((message) =&gt; {
 console.log(message)
 })
}
</code></pre>

Or you could try use <code>Promise.all()</code> which will basically solve the order for you, see the official <a href="https://developer.mozilla.org/fr/docs/Web/JavaScript/Reference/Objets_globaux/Promise/all" rel="nofollow noreferrer">docs here</a>

blocks|key|3958138|text|我在这里找到了一个解决方案：MDN+promise+then|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|3958139|for+(let+i+=+0;+i+<+10;+i%2B%2B)+{
++++let+p+=+new+Promise((resolve,+reject)+=>+{
++++++++let+a+=+1+%2B+(i+%25+2)

++++++++if+(a+===+2)+{
++++++++++++resolve(i+%2B+'+resolve+'+%2B+a)
++++++++}+else+{
++++++++++++reject(i+%2B+'+reject+'+%2B+a)
++++++++}
++++})

++++p.then((message)+=>+{
++++++++console.log(message)
++++},+failed+=>+{
++++++++console.log(failed)
++++})+
}|code-block|syntax|javascript|3958140|promise.catch()正在调用promise.then(未定义，onreject)。这就是为什么resolve总是首先出现的原因。|3958141|entityMap|0|LINK|mutability|MUTABLE|url|https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise/then^0|E|G|0|0|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@$A|T|B|U|1|V]]|C|$]]|$1|D|3|E|5|F|7|W|8|@]|9|@]|C|$G|H]]|$1|I|3|J|5|6|7|X|8|@]|9|@]|C|$]]|$1|K|3|-4|5|6|7|Y|8|@]|9|@]|C|$]]]|L|$M|$5|N|O|P|C|$Q|R]]]]

I did found a solution here:
<a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise/then" rel="nofollow noreferrer">MDN promise then</a>

<pre><code>for (let i = 0; i &lt; 10; i++) {
 let p = new Promise((resolve, reject) =&gt; {
 let a = 1 + (i % 2)

 if (a === 2) {
 resolve(i + ' resolve ' + a)
 } else {
 reject(i + ' reject ' + a)
 }
 })

 p.then((message) =&gt; {
 console.log(message)
 }, failed =&gt; {
 console.log(failed)
 }) 
}
</code></pre>

promise.catch() is calling promise.then(undefined, onreject). That is why resolve allways appeared first.

I'm trying to wrap my mind around promises in JavaScript. I was under the illusion that once a Promise was resolved it could never go back to rejected. To test that I wrote a little script. I see that the first messages that come back are the resolve messages "1 resolve 2" etc. I expected the first message to be "0 reject 1".

<pre><code>for (let i = 0; i &lt; 10; i++) {
 let p = new Promise((resolve, reject) =&gt; {

 let a = 1 + (i % 2)

 if (a === 2) {
 resolve(i + ' resolve ' + a)
 } else {
 reject(i + ' reject ' + a)
 } 
 })

 p.then((message) =&gt; {
 console.log(message)
 }).catch((message) =&gt; {
 console.log(message)
 })
}
</code></pre>

at the console:

<pre><code>[Log] 1 resolve 2
[Log] 3 resolve 2
[Log] 5 resolve 2
[Log] 7 resolve 2
[Log] 9 resolve 2
[Log] 0 reject 1
[Log] 2 reject 1
[Log] 4 reject 1
[Log] 6 reject 1
[Log] 8 reject 1
&lt; Promise {status: "pending"}
</code></pre>

thanks for you help....

After reading 

<a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise/then" rel="nofollow noreferrer">https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise/then</a>

I got to this code. The catch is removed.

<pre><code>for (let i = 0; i &lt; 10; i++) {
let p = new Promise((resolve, reject) =&gt; {

 let a = 1 + (i % 2)

 if (a === 2) {
 resolve(i + ' resolve ' + a)
 } else {
 reject(i + ' reject ' + a)
 }

})

p.then((message) =&gt; {
 console.log(message)
}, failed =&gt; {
 console.log(failed)
}) 
}
</code></pre>

at the console:

<pre><code>[Log] 0 reject 1
[Log] 1 resolve 2
[Log] 2 reject 1
[Log] 3 resolve 2
[Log] 4 reject 1
[Log] 5 resolve 2
[Log] 6 reject 1
[Log] 7 resolve 2
[Log] 8 reject 1
[Log] 9 resolve 2
&lt; Promise {status: "pending"}
</code></pre>

Why does the resolve message appear first?

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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我正试着把注意力集中在JavaScript中的承诺上。我有一种错觉，认为一旦一个承诺被解决了，它就再也不会被拒绝了。为了测试我写了一个小脚本。我看到返回的第一个消息是resolve消息"1 resolve 2“等等。我希望第一个消息是"0 reject 1”。for (let i = 0; i < 10; i++) {...

问为什么首先出现resolve消息？
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