blocks|key|5007254|text|只需检查files属性的长度，它是包含在输入元素上的FileList对象。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|5007255|if(+document.getElementById("videoUploadFile").files.length+==+0+){
++++console.log("no+files+selected");
}|code-block|syntax|javascript|5007256|entityMap|0|LINK|mutability|MUTABLE|url|https://developer.mozilla.org/en-US/docs/Web/API/FileList#Attributes|1|https://developer.mozilla.org/en-US/docs/Web/API/FileList^0|4|5|0|Q|8|1|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@$A|T|B|U|1|V]|$A|W|B|X|1|Y]]|C|$]]|$1|D|3|E|5|F|7|Z|8|@]|9|@]|C|$G|H]]|$1|I|3|-4|5|6|7|10|8|@]|9|@]|C|$]]]|J|$K|$5|L|M|N|C|$O|P]]|Q|$5|L|M|N|C|$O|R]]]]

<p>Just check the length of <a href="https://developer.mozilla.org/en-US/docs/Web/API/FileList#Attributes">files</a> property, which is a <a href="https://developer.mozilla.org/en-US/docs/Web/API/FileList">FileList</a> object contained on the input element</p>

<pre><code>if( document.getElementById("videoUploadFile").files.length == 0 ){
    console.log("no files selected");
}
</code></pre>


blocks|key|5007265|text|下面是它的jQuery版本：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|5007266|if+($('#videoUploadFile').get(0).files.length+===+0)+{
++++console.log("No+files+selected.");
}|code-block|syntax|javascript|5007267|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

<p>Here is the jQuery version of it:</p>

<pre><code>if ($('#videoUploadFile').get(0).files.length === 0) {
    console.log("No files selected.");
}
</code></pre>


blocks|key|5007323|text|若要使用“文件长度”属性检查输入文件是否为空，应指定index，如下所示：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|5007324|var+vidFileLength+=+$("#videoUploadFile")[0].files.length;
if(vidFileLength+===+0){
++++alert("No+file+selected.");
}|code-block|syntax|javascript|5007325|entityMap^0|Q|5|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@$9|N|A|O|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|P|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|Q|8|@]|D|@]|E|$]]]|L|$]]

<p>To check whether the input file is empty or not
by using the file length property, <code>index</code> should be specified like the following:</p>

<pre><code>var vidFileLength = $("#videoUploadFile")[0].files.length;
if(vidFileLength === 0){
    alert("No file selected.");
}
</code></pre>


blocks|key|5696291|text|我知道我要迟到了，但我想我应该添加我最后为此使用的内容--这就是简单地检查文件上传输入是否包含非操作符的真实值&+JQuery如下所示：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|5696292|if+(!$('#videoUploadFile').val())+{
++alert('Please+Upload+File');
}|code-block|syntax|javascript|5696293|请注意，如果这是在表单中，您还可能希望用以下处理程序包装它，以防止表单提交：|5696294|$(document).on("click",+":submit",+function+(e)+{

++if+(!$('#videoUploadFile').val())+{
++e.preventDefault();
++alert('Please+Upload+File');
++}

}|5696295|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|N|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|O|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

<p>I know I'm late to the party but I thought I'd add what I ended up using for this - which is to simply check if the file upload input does not contain a truthy value with the not operator &amp; JQuery like so:</p>

<pre><code>if (!$('#videoUploadFile').val()) {
  alert('Please Upload File');
}
</code></pre>

<p>Note that if this is in a form, you may also want to wrap it with the following handler to prevent the form from submitting:</p>

<pre><code>$(document).on("click", ":submit", function (e) {

  if (!$('#videoUploadFile').val()) {
  e.preventDefault();
  alert('Please Upload File');
  }

}
</code></pre>


blocks|key|86953|text|问题:如何检查文件是否为空？|type|unstyled|depth|inlineStyleRanges|entityRanges|data|86954|答:我使用Jquery代码解决了这个问题。|86955|​|86956|//If+your+file+Is+Empty+:+++++
++++++if+(jQuery('#videoUploadFile').val()+==+'')+{
+++++++++++++++++++++++$('#message').html("Please+Attach+File");
+++++++++++++++++++}else+{
++++++++++++++++++++++++++++alert('not+work');
+++++++++++++++++++}|code-block|syntax|javascript|86957|<script+src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<input+type="file"+id="videoUploadFile">
<br>
<br>
<div+id="message"></div>|86958|86959|entityMap^0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|P|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|Q|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|R|8|@]|9|@]|A|$]]|$1|F|3|G|5|H|7|S|8|@]|9|@]|A|$I|J]]|$1|K|3|L|5|H|7|T|8|@]|9|@]|A|$I|J]]|$1|M|3|E|5|6|7|U|8|@]|9|@]|A|$]]|$1|N|3|-4|5|6|7|V|8|@]|9|@]|A|$]]]|O|$]]

<p>Questions : how to check File is empty or not? </p>

<p>Ans:  I have slove this issue using this Jquery 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>//If your file Is Empty :     
      if (jQuery('#videoUploadFile').val() == '') {
                       $('#message').html("Please Attach File");
                   }else {
                            alert('not work');
                   }

    </code></pre>
<pre class="snippet-code-html lang-html prettyprint-override"><code>&lt;script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"&gt;&lt;/script&gt;
&lt;input type="file" id="videoUploadFile"&gt;
&lt;br&gt;
&lt;br&gt;
&lt;div id="message"&gt;&lt;/div&gt;</code></pre>
</div>
</div>
</p>


blocks|key|89189|text|++$("#customFile").change(function()+{+
++++var+fileName+=+$("#customFile").val();++

++++if(fileName)+{+//+returns+true+if+the+string+is+not+empty+++
++++++++$('.picture-selected').addClass('disable-inputs');+
++++++++$('#btn').removeClass('disabled');+++
++++}+else+{+//+no+file+was+selected+
++++++$('.picture-selected').removeClass('disable-inputs');+
++++++$('#btn').addClass('disabled');
++++}++
++});|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|89190|unstyled|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|G|8|@]|9|@]|A|$B|C]]|$1|D|3|-4|5|E|7|H|8|@]|9|@]|A|$]]]|F|$]]

<pre><code>  $(&quot;#customFile&quot;).change(function() { 
    var fileName = $(&quot;#customFile&quot;).val();  

    if(fileName) { // returns true if the string is not empty   
        $('.picture-selected').addClass('disable-inputs'); 
        $('#btn').removeClass('disabled');   
    } else { // no file was selected 
      $('.picture-selected').removeClass('disable-inputs'); 
      $('#btn').addClass('disabled');
    }  
  });
</code></pre>


blocks|key|5007393|text|if+(data.name+==+'')+{
+++//file+doesn't+exist;
}
else+{
+++//file+exist;
}|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|5007394|unstyled|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|G|8|@]|9|@]|A|$B|C]]|$1|D|3|-4|5|E|7|H|8|@]|9|@]|A|$]]]|F|$]]

<pre><code>if (data.name == '') {
   //file doesn't exist;
}
else {
   //file exist;
}
</code></pre>


<p>Brand new to JS.<br>
I am trying to check if the file input element is empty when submitting the form with jQuery/JavaScript.
I have gone through a bunch of solutions and nothing is working for me.  I am trying to avoid the <code>/c/fakepath</code> (unless there is no other option)</p>

<pre><code>&lt;input type="file" name="videoFile" id="videoUploadFile" /&gt;
</code></pre>

<p>This does not work:</p>

<pre><code>var vidFile = $("#videoUploadFile").value;
</code></pre>

<p>The only way I can get the filename is if I use the following:</p>

<pre><code>var vidFile = document.getElementById("videoUploadFile").files[0].name;
</code></pre>

<p>If there is no file available the code throws an error: </p>

<blockquote>
  <p>cannot read property name of undefined</p>
</blockquote>

<p>which makes sense because the array is not set. but I cannot figure out how to do any error handling with this.</p>

<p>How do I properly grab the file input element <code>videoUploadFile</code>, check if it's empty, throw an error message if it's empty?</p>


How to check if input file is empty in jQuery

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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对JS来说是全新的。在用jQuery/JavaScript提交表单时，我试图检查文件输入元素是否为空。我经历了一堆解决方案，但对我没有任何作用。我试图避免/c/fakepath (除非没有其他选择)<input type="file" name="videoFile" id="videoUploadFile" />这样做是行不通的：var vidFile = $("#videoUploadFile

问如何在jQuery中检查输入文件是否为空
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