blocks|key|2461602|text|正如注释所说，代码不等待，它异步运行。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2461603|您有两个选项：|2461604|1)在test2()函数中使用setTimeout，如：|offset|length|style|CODE|2461605|function+test2()+{
+++setTimeout(function()+{
+++++++console.log(jeff);
+++},+1000);
}|code-block|syntax|javascript|2461606|2)或者调用test2()时使用setTimeout，如下所示：|2461607|setTimeout(function()+{
+++console.log(jeff);
},+1000);|2461608|这两者的行为是完全相同的。|2461609|entityMap^0|0|0|3|7|F|A|0|0|6|7|G|A|0|0|0^^$0|@$1|2|3|4|5|6|7|W|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|X|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|Y|8|@$F|Z|G|10|H|I]|$F|11|G|12|H|I]]|9|@]|A|$]]|$1|J|3|K|5|L|7|13|8|@]|9|@]|A|$M|N]]|$1|O|3|P|5|6|7|14|8|@$F|15|G|16|H|I]|$F|17|G|18|H|I]]|9|@]|A|$]]|$1|Q|3|R|5|L|7|19|8|@]|9|@]|A|$M|N]]|$1|S|3|T|5|6|7|1A|8|@]|9|@]|A|$]]|$1|U|3|-4|5|6|7|1B|8|@]|9|@]|A|$]]]|V|$]]

<p>As per the comments say, the code doesn't wait, it runs asynchronous.</p>

<p>You have 2 options:</p>

<p>1) Use a <code>setTimeout</code> in the <code>test2()</code> function, like so:</p>

<pre><code>function test2() {
   setTimeout(function() {
       console.log(jeff);
   }, 1000);
}
</code></pre>

<p>2) Or use a <code>setTimeout</code> when calling <code>test2()</code>, like so:</p>

<pre><code>setTimeout(function() {
   console.log(jeff);
}, 1000);
</code></pre>

<p>Both of these will act exactly the same...</p>


blocks|key|2144333|text|只有在超时期间或之后发生调用console.log的console.log或函数时，才能使其正常工作。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|2144334|例如：|2144335|​|2144336|var+jeff+=+"before";

function+test()+{
++setTimeout(function()+{
++++jeff+=+"after";
++++test2();
++},+1000);
}

test();

function+test2()+{
++console.log(jeff);
}|code-block|syntax|javascript|2144337|2144338|entityMap^0|E|B|Q|B|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|R|8|@$9|S|A|T|B|C]|$9|U|A|V|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|W|8|@]|D|@]|E|$]]|$1|H|3|I|5|6|7|X|8|@]|D|@]|E|$]]|$1|J|3|K|5|L|7|Y|8|@]|D|@]|E|$M|N]]|$1|O|3|I|5|6|7|Z|8|@]|D|@]|E|$]]|$1|P|3|-4|5|6|7|10|8|@]|D|@]|E|$]]]|Q|$]]

<p>The only way you will get this to work is if you cause the <code>console.log</code>or a function that calls <code>console.log</code> to happen during or after the timeout.</p>

<p>For example:</p>

<p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
<div class="snippet-code">
<pre class="snippet-code-js lang-js prettyprint-override"><code>var jeff = "before";

function test() {
  setTimeout(function() {
    jeff = "after";
    test2();
  }, 1000);
}

test();

function test2() {
  console.log(jeff);
}

   </code></pre>
</div>
</div>
</p>


blocks|key|16608|text|正如评论者指出的那样，setTimeout导致该代码块(+setTimeout回调函数)异步运行，这意味着主“线程”(抱歉，这里不是恰当的术语)继续运行，而不使用它，在您的例子中，线程是test1()和test2()的执行。显然，这一切都发生在不到1000毫秒的时间里，所以你的全局变量仍然是“之前”。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|16609|然而，这里还有更多的事情要做:尝试将超时更改为0。你会注意到它仍然不能工作。这是因为异步代码必须在队列中等待，然后才有机会执行。主“线程”在没有它的情况下仍然会继续运行，因为这就好像在那个setTimeout中运行代码有两个标准:+1.指定的毫秒必须已经过去，2.线程/栈/东西应该不忙。如果在时间到期时它很忙，您的代码仍然必须等待，直到事件循环在另一个时间返回时，才能空闲地执行该代码。|16610|如果技术术语不准确，很抱歉。我认为从概念上讲，这应该是非常有帮助的。这里有一个很棒的视频，可以让你深入了解一下：https://youtu.be/cCOL7MC4Pl0|16611|entityMap|0|LINK|mutability|MUTABLE|url|https://youtu.be/cCOL7MC4Pl0^0|2L|7|2T|7|0|0|1K|S|0|0^^$0|@$1|2|3|4|5|6|7|R|8|@$9|S|A|T|B|C]|$9|U|A|V|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|W|8|@]|D|@]|E|$]]|$1|H|3|I|5|6|7|X|8|@]|D|@$9|Y|A|Z|1|10]]|E|$]]|$1|J|3|-4|5|6|7|11|8|@]|D|@]|E|$]]]|K|$L|$5|M|N|O|E|$P|Q]]]]

<p>As commenters are pointing out, the setTimeout causes that block of code (the setTimeout callback function) to run asynchronously, which means that the main “thread” (sorry if that’s not the proper term here) continues to run without it, which in your case is the execution of <code>test1()</code> and <code>test2()</code>. Obviously that all happens in less than 1000 milliseconds, so your global variable is still “before”.</p>

<p>HOWEVER, there is more going on here: try changing the timeout to 0. You’ll notice that it still doesn’t work. That is because asynchronous code must wait in a queue before it has a chance to be executed. The main “thread” will still continue running without it, because it’s as if there are two criteria for running code within that setTimeout: 1. The specified milliseconds must have passed, and 2. the thread/stack/thing shouldn’t be busy. If it is busy when the time is up, your code will still have to wait until the event loop comes back around another time with a free hand to execute that code.</p>

<p>Sorry if the technical jargon isn’t exact. I think conceptually that should be very helpful. Here is an excellent video which will give you a look under the hood: <a href="https://youtu.be/cCOL7MC4Pl0" rel="nofollow noreferrer">https://youtu.be/cCOL7MC4Pl0</a></p>


<p>I'm trying to overwrite a variable using a global variable from within a function, however, it doesn't seem to be working and I can't figure out why.</p>

<p>I want the end result in test2 to log "after". It's currently logging "before".</p>

<p>If I remove the setTimeout it works, however, I need a setTimeout in the code.</p>

<p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
<div class="snippet-code">
<pre class="snippet-code-js lang-js prettyprint-override"><code>var jeff = "before";

function test() {
  setTimeout(function() {
    jeff = "after";
    test();
  }, 1000);
}

test();

function test2() {
  console.log(jeff);
}

test2();</code></pre>
</div>
</div>
</p>

<p>Thanks!</p>


Javascript overwriting a variable inside setTimeout anon function

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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我试图用一个函数中的全局变量覆盖一个变量，但是，它似乎不起作用，我也不知道为什么。我希望test2中的最终结果记录为"after“。它目前记录的是“之前”。但是，如果我删除setTimeout就可以工作，我需要在代码中使用setTimeout。​var jeff = "before";function test() {...

问Javascript覆盖setTimeout anon函数中的变量
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