blocks|key|1440211|text|如果服务器没有响应，fetch将其作为connection+failure并在catch()块中处理。fetch只在连接成功时执行then()块。如果连接未成功，则将执行catch()块。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1440212|fetch('something')
+.then(+response+=>+{})
+.catch(error+=>+{
+++//+handle+error+here
+})|code-block|syntax|javascript|1440213|检查提取是否成功|1440214|entityMap|0|LINK|mutability|MUTABLE|url|https://developer.mozilla.org/en-US/docs/Web/API/Fetch_API/Using_Fetch#checking_that_the_fetch_was_successful^0|A|5|J|I|13|7|1F|5|1T|6|2D|7|0|0|0|8|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@$9|V|A|W|B|C]|$9|X|A|Y|B|C]|$9|Z|A|10|B|C]|$9|11|A|12|B|C]|$9|13|A|14|B|C]|$9|15|A|16|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|17|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|18|8|@]|D|@$9|19|A|1A|1|1B]]|E|$]]|$1|M|3|-4|5|6|7|1C|8|@]|D|@]|E|$]]]|N|$O|$5|P|Q|R|E|$S|T]]]]

If the server doesn't respond, <code>fetch</code> takes it as <code>connection failure</code> and handles it in the <code>catch()</code> block. The <code>fetch</code> only executes <code>then()</code> blocks when the connection is successful. If the connection was not successful, the <code>catch()</code> block will be executed.
<pre><code>fetch('something')
 .then( response =&gt; {})
 .catch(error =&gt; {
 // handle error here
 })
</code></pre>
<a href="https://developer.mozilla.org/en-US/docs/Web/API/Fetch_API/Using_Fetch#checking_that_the_fetch_was_successful" rel="nofollow noreferrer">Checking that fetch was successful</a>

blocks|key|719314|text|你在找渔获物。在catch块中，您可以获取错误。下面的示例您可以访问error对象。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|719315|​|719316|fetch("https://rockosmodernserver.westus2.cloudapp.azure.com/+",+{
++++method:+"GET",
++++}).then(response+=>+response)
++++.then(data+=>+{
++++++++console.log("server+is+up")
++++})
++++.catch((error)+=>+{
++++++console.error('Error:',+error);
++++++console.log("server+is+down!!")+++
++++});|code-block|syntax|javascript|719317|719318|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|L|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|M|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|N|8|@]|9|@]|A|$G|H]]|$1|I|3|C|5|6|7|O|8|@]|9|@]|A|$]]|$1|J|3|-4|5|6|7|P|8|@]|9|@]|A|$]]]|K|$]]

You looking for catch block. In the catch block you can fetch the errors. Imn the example below you have access to the error object.
<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>fetch("https://rockosmodernserver.westus2.cloudapp.azure.com/ ", {
 method: "GET",
 }).then(response =&gt; response)
 .then(data =&gt; {
 console.log("server is up")
 })
 .catch((error) =&gt; {
 console.error('Error:', error);
 console.log("server is down!!") 
 });</code></pre>
</div>
</div>

blocks|key|1440284|text|如果服务器不接，他就不能给你答复。这意味着没有状态代码。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1440285|更新:当遇到网络错误或服务器端的CORS配置错误时，()承诺将拒绝TypeError，尽管这通常意味着权限问题或类似的问题-例如，404并不构成网络错误。对成功的fetch()的准确检查将包括检查承诺是否已解决，然后检查Response.ok属性的值是否为true。代码应该如下所示：|offset|length|style|BOLD|1440286|++fetch('flowers.jpg')
++.then(response+=>+{
++++if+(!response.ok)+{
++++++throw+new+Error('Network+response+was+not+OK');
++++}
++++return+response.blob();
++})
++.then(myBlob+=>+{
++++myImage.src+=+URL.createObjectURL(myBlob);
++})
++.catch(error+=>+{
++++console.error('There+has+been+a+problem+with+your+fetch+operation:',+error);
++});|code-block|syntax|javascript|1440287|成功|1440288|第一次编辑:通过使用超时并跟踪超时的发生，这个解决方案可能会有所帮助。https://stackoverflow.com/a/50101022/13111978|1440289|entityMap|0|LINK|mutability|MUTABLE|url|https://developer.mozilla.org/en-US/docs/Web/API/Fetch_API/Using_Fetch#checking_that_the_fetch_was_successful|1|https://stackoverflow.com/a/50101022/13111978^0|0|0|Q|0|0|0|2|0|0|0|L|Z|19|1|0^^$0|@$1|2|3|4|5|6|7|10|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|11|8|@$D|12|E|13|F|G]]|9|@]|A|$]]|$1|H|3|I|5|J|7|14|8|@]|9|@]|A|$K|L]]|$1|M|3|N|5|6|7|15|8|@]|9|@$D|16|E|17|1|18]]|A|$]]|$1|O|3|P|5|6|7|19|8|@$D|1A|E|1B|F|G]]|9|@$D|1C|E|1D|1|1E]]|A|$]]|$1|Q|3|-4|5|6|7|1F|8|@]|9|@]|A|$]]]|R|$S|$5|T|U|V|A|$W|X]]|Y|$5|T|U|V|A|$W|Z]]]]

If a server is not answering, he can not give you a response.
Which means there is no status code.
Update:
A fetch() promise will reject with a TypeError when a network error is encountered or CORS is misconfigured on the server-side, although this usually means permission issues or similar — a 404 does not constitute a network error, for example. An accurate check for a successful fetch() would include checking that the promise resolved, then checking that the Response.ok property has a value of true. The code would look something like this:
<pre><code> fetch('flowers.jpg')
 .then(response =&gt; {
 if (!response.ok) {
 throw new Error('Network response was not OK');
 }
 return response.blob();
 })
 .then(myBlob =&gt; {
 myImage.src = URL.createObjectURL(myBlob);
 })
 .catch(error =&gt; {
 console.error('There has been a problem with your fetch operation:', error);
 });
</code></pre>
<a href="https://developer.mozilla.org/en-US/docs/Web/API/Fetch_API/Using_Fetch#checking_that_the_fetch_was_successful" rel="nofollow noreferrer">https://developer.mozilla.org/en-US/docs/Web/API/Fetch_API/Using_Fetch#checking_that_the_fetch_was_successful</a>
First edit:
This solution could be helpful, by using a timeout and track that timeout has happened.
<a href="https://stackoverflow.com/a/50101022/13111978">https://stackoverflow.com/a/50101022/13111978</a>

I must be getting old google searches because I can't find any threads on how to do this if you are using javascript's <code>fetch</code> not the old <code>XMLHttpRequest</code>
I am trying to test whether or not my VM is online. The rest of the VM is locked down but I left an open endpoint for testing.
I tried using the <code>status</code> to check if the server is up but gave me a different error than a response error:
<pre><code>fetch(&quot;https://rockosmodernserver.westus2.cloudapp.azure.com/ &quot;, {
 method: &quot;GET&quot;,
 }).then(response =&gt; response)
 .then(data =&gt; {
 if (data.status == 200){
 console.log(&quot;server is up&quot;)
 }
 else{
 console.log(&quot;server is down!!&quot;) 
 }
 })
</code></pre>
It works if the server is up but if the server is down I get:
<pre><code>VM739:1 GET https://rockosmodernserver.westus2.cloudapp.azure.com/ net::ERR_CONNECTION_REFUSED
</code></pre>
when I tried googling this I got solutions for <code>XMLHttpRequest</code> but not for the fetch module.

catch fetch ERR_CONNECTION_REFUSED

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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我一定是在使用旧的google搜索，因为如果您使用javascript的fetch，而不是旧的XMLHttpRequest，我就找不到关于如何执行此操作的线程。我正在试着测试我的VM是否在线。VM的其余部分被锁定，但我留下了一个开放的端点进行测试。我尝试使用status来检查服务器是否已启动，但给出了一个与响应错误不同...

问捕获获取ERR_CONNECTION_REFUSED
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