blocks|key|127089|text|不能在forEach周期中使用async/await。你可以在一个简单的for循环或一段时间内使用它，做...|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|127090|例如：|127091|export+async+function+asyncForEach(array,+callback)+{
++for+(let+index+=+0;+index+<+array.length;+index%2B%2B)+{
++++await+callback(array[index],+index,+array);
++}
}|code-block|syntax|javascript|127092|entityMap^0|3|7|F|B|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@$9|P|A|Q|B|C]|$9|R|A|S|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|T|8|@]|D|@]|E|$]]|$1|H|3|I|5|J|7|U|8|@]|D|@]|E|$K|L]]|$1|M|3|-4|5|6|7|V|8|@]|D|@]|E|$]]]|N|$]]

The <code>async/await</code> cannot be used in <code>forEach</code> cycle.
You can use it in a simple for cycle or a while, do ...
For example:
<pre class="lang-js prettyprint-override"><code>export async function asyncForEach(array, callback) {
 for (let index = 0; index &lt; array.length; index++) {
 await callback(array[index], index, array);
 }
}
</code></pre>

blocks|key|127077|text|每当您看到像.forEach(async+(trId)+=>+{这样的异步回调时，出现问题的可能性都很高。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|127078|问题是，async函数实际上是promises，因此它们不会阻塞主线程。这意味着您的回调函数将在作业队列中排队，并将在将来执行。|127079|它是这样简化的：|127080|let+arr+=+[]
setTimeout(()+=>+{
+++arr.push("hy")
})
console.log(arr)|code-block|syntax|javascript|127081|arr将简单地为空，|127082|但是，您可以使用for+...+of循环|127083|const+generateCatReports+=+async+(
++mode+=+"monthly",
++months+=+1,
++toDate+=+false
)+=>+{
++if+(!["monthly",+"weekly"].includes(mode))+{
++++throw+new+Error(InvalidParamsError);
++}
++const+sortedTRIds+=+obtainSortedCentreIds(studiesTRMap,+centreNameIDMap);
++const+modRows+=+[];
++for+(const+trId+of+sortedTRIds)+{
++++const+statsParams+=+{
++++++catId:+trId,
++++++createdAt
++++};
++++const+statsPipeline+=+studiesStatsPipeline(statsParams,+capitalize(mode));
++++const+statsInfo+=+await+StudyModel.aggregate(statsPipeline)
++++++.allowDiskUse(true)
++++++.exec();
++++Object.entries(statsInfo[0])
++++++.slice(1)
++++++.forEach(([key,+val])+=>+{
++++++++modRows.push([key,+val]);
++++++});
++++console.log("inside+sortedTr+loop>>>>>",+modRows);
++}
++console.log("outside+sortedTr+loop>>>>>>>>",+modRows);
};|127084|在这里，您没有要排队的回调。|127085|更好的解决方案是使用Promise.all()|127086|const+generateCatReports+=+async+(
++mode+=+"monthly",
++months+=+1,
++toDate+=+false
)+=>+{
++if+(!["monthly",+"weekly"].includes(mode))+{
++++throw+new+Error(InvalidParamsError);
++}
++const+sortedTRIds+=+obtainSortedCentreIds(studiesTRMap,+centreNameIDMap);
++const+modRows+=+await+Promise.all(
++++sortedTRIds.flatMap(async+(trId)+=>+{
++++++const+statsParams+=+{
++++++++catId:+trId,
++++++++createdAt
++++++};
++++++const+statsPipeline+=+studiesStatsPipeline(statsParams,+capitalize(mode));
++++++const+statsInfo+=+await+StudyModel.aggregate(statsPipeline)
++++++++.allowDiskUse(true)
++++++++.exec();
++++++return+Object.entries(statsInfo[0]).slice(1);
++++})
++);

++console.log(modRows);
};|127087|entityMap^0|6|Q|0|4|5|0|0|0|0|8|A|0|0|0|A|D|0|0^^$0|@$1|2|3|4|5|6|7|12|8|@$9|13|A|14|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|15|8|@$9|16|A|17|B|C]]|D|@]|E|$]]|$1|H|3|I|5|6|7|18|8|@]|D|@]|E|$]]|$1|J|3|K|5|L|7|19|8|@]|D|@]|E|$M|N]]|$1|O|3|P|5|6|7|1A|8|@]|D|@]|E|$]]|$1|Q|3|R|5|6|7|1B|8|@$9|1C|A|1D|B|C]]|D|@]|E|$]]|$1|S|3|T|5|L|7|1E|8|@]|D|@]|E|$M|N]]|$1|U|3|V|5|6|7|1F|8|@]|D|@]|E|$]]|$1|W|3|X|5|6|7|1G|8|@$9|1H|A|1I|B|C]]|D|@]|E|$]]|$1|Y|3|Z|5|L|7|1J|8|@]|D|@]|E|$M|N]]|$1|10|3|-4|5|6|7|1K|8|@]|D|@]|E|$]]]|11|$]]

Whenever you see an async callback like <code>.forEach(async (trId) =&gt; {</code> the chance that something is wrong is pretty high.
The problem what you have is that <code>async</code> functions are actually promises and therefore they don't block the main thread. That means that your callback function gets queued in the job queue and will be executed in the future.
Its simplified the same like this:
<pre><code>let arr = []
setTimeout(() =&gt; {
 arr.push(&quot;hy&quot;)
})
console.log(arr)
</code></pre>
arr will be simply empty,
However you can use an <code>for ... of</code> loop
<pre><code>const generateCatReports = async (
 mode = &quot;monthly&quot;,
 months = 1,
 toDate = false
) =&gt; {
 if (![&quot;monthly&quot;, &quot;weekly&quot;].includes(mode)) {
 throw new Error(InvalidParamsError);
 }
 const sortedTRIds = obtainSortedCentreIds(studiesTRMap, centreNameIDMap);
 const modRows = [];
 for (const trId of sortedTRIds) {
 const statsParams = {
 catId: trId,
 createdAt
 };
 const statsPipeline = studiesStatsPipeline(statsParams, capitalize(mode));
 const statsInfo = await StudyModel.aggregate(statsPipeline)
 .allowDiskUse(true)
 .exec();
 Object.entries(statsInfo[0])
 .slice(1)
 .forEach(([key, val]) =&gt; {
 modRows.push([key, val]);
 });
 console.log(&quot;inside sortedTr loop&gt;&gt;&gt;&gt;&gt;&quot;, modRows);
 }
 console.log(&quot;outside sortedTr loop&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&quot;, modRows);
};
</code></pre>
Here you have no callback that will be queued.
A better solution would be to use <code>Promise.all()</code>
<pre><code>const generateCatReports = async (
 mode = &quot;monthly&quot;,
 months = 1,
 toDate = false
) =&gt; {
 if (![&quot;monthly&quot;, &quot;weekly&quot;].includes(mode)) {
 throw new Error(InvalidParamsError);
 }
 const sortedTRIds = obtainSortedCentreIds(studiesTRMap, centreNameIDMap);
 const modRows = await Promise.all(
 sortedTRIds.flatMap(async (trId) =&gt; {
 const statsParams = {
 catId: trId,
 createdAt
 };
 const statsPipeline = studiesStatsPipeline(statsParams, capitalize(mode));
 const statsInfo = await StudyModel.aggregate(statsPipeline)
 .allowDiskUse(true)
 .exec();
 return Object.entries(statsInfo[0]).slice(1);
 })
 );

 console.log(modRows);
};
</code></pre>

blocks|key|130723|text|这就是为什么你不应该在forEach循环中使用异步/等待，|type|unstyled|depth|inlineStyleRanges|entityRanges|data|130724|forEach循环接受回调，即使您将异步函数作为回调传递也不会等待。异步回调将等待它内部的任何承诺，但forEach循环将继续为数组中的所有元素执行回调函数。|130725|而不是使用for...in循环，正如预期的那样，for...in循环内部的等待将停止循环执行，并仅在您完成对promise的等待时才继续迭代。|offset|length|style|CODE|130726|entityMap^0|0|0|5|8|O|8|0^^$0|@$1|2|3|4|5|6|7|L|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|M|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|N|8|@$F|O|G|P|H|I]|$F|Q|G|R|H|I]]|9|@]|A|$]]|$1|J|3|-4|5|6|7|S|8|@]|9|@]|A|$]]]|K|$]]

This is why you should not use async/await in forEach loop,
forEach loop accepts a callback, and won't wait even if you pass an async function as callback. Your async callback will wait for any promises inside of it but forEach loop will keep on executing callback function for all the elements in the array.
instead use <code>for...in</code> loop, as expected, an await inside of <code>for...in</code> loop will halt the loop execution and only continue iterating when you're done awaiting on a promise.

I'm trying to add a table in my existing code for some data and for this i have setted up everything similar to what mentioned in the exceljs docs. Here is a code snippet of the condition where i'm trying to get the data i need in order to get the table. When i'm printing the modRows within the forEach, it's showing the data but when i'm printing it outside the loop it's getting blank. Is there any way or other workaround to this? Is it possible to have async within async?
<pre><code>const generateCatReports = async (mode = 'monthly', months = 1, toDate = false) =&gt; {
 if (!['monthly', 'weekly'].includes(mode)) {
 throw new Error(InvalidParamsError);
 }
 const sortedTRIds = obtainSortedCentreIds(studiesTRMap, centreNameIDMap);
 const modRows = [];
 sortedTRIds.forEach(async (trId) =&gt; {
 console.log(&quot;trid&quot;,trId);
 const statsParams = {
 catId: trId,
 createdAt,
 };
 const statsPipeline = studiesStatsPipeline(statsParams, capitalize(mode));
 const statsInfo = await StudyModel.aggregate(statsPipeline).allowDiskUse(true).exec();
 Object.entries(statsInfo[0]).slice(1).forEach(([key, val]) =&gt; {
 modRows.push([key, val]);
 });
 console.log(&quot;inside sortedTr loop&gt;&gt;&gt;&gt;&gt;&quot; ,modRows);
 });
 console.log(&quot;outside sortedTr loop&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&quot;,modRows);

}
</code></pre>
Result:
<pre><code>trId 1cf1eb1324322bbebe
inside sortedTr loop&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;
['TOTAL', 10]
['white', 5]
['black', 5]

trId 1cf1eb1324322bbebe
inside sortedTr loop&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;
['TOTAL', 10]
['white', 5]
['black', 5]

trId 21e1eb21322bbebe
inside sortedTr loop&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;
['TOTAL', 8]
['white', 6]
['black', 2]

outside sortedTr loop&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;&gt;
[]
</code></pre>

Nested async await not working as expected

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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我试图在我现有的代码中为一些数据添加一个表，为此，我已经设置了类似于exceljs文档中提到的所有内容。下面是我试图获取所需数据以获取表的条件的代码片段。当我在forEach中打印modRows时，它显示的是数据，但是当我在循环之外打印它时，它变得空白。有没有什么办法或者其他解决办法呢？是否可以在异步中使用异步？con...

问嵌套异步等待未按预期工作
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