entityMap|blocks|key|2n498|text|if+($(".mydivclass").size()){
+++//+code+here
}|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|f271l|size()方法只返回jQuery选择器选择的元素的数量-在本例中是包含类的元素的数量mydivclass。如果返回0，则表达式为false，因此没有表达式；如果返回任何其他数字，则div必须存在。|unstyled|offset|length|style|CODE^0|0|0|6|17|A^^$0|$]|1|@$2|3|4|5|6|7|8|L|9|@]|A|@]|B|$C|D]]|$2|E|4|F|6|G|8|M|9|@$H|N|I|O|J|K]|$H|P|I|Q|J|K]]|A|@]|B|$]]]]

<pre><code>if ($(".mydivclass").size()){
 // code here
}
</code></pre>

The <code>size()</code> method just returns the number of elements that the jQuery selector selects - in this case the number of elements with the class <code>mydivclass</code>. If it returns 0, the expression is false, and therefore there are none, and if it returns any other number, the divs must exist.

entityMap|blocks|key|1b73t|text|检查div是否存在某个类|type|unstyled|depth|inlineStyleRanges|entityRanges|data|90lum|if+($(".mydivclass").length+>+0)+//it+exists+
{

}|code-block|syntax|javascript^0|0^^$0|$]|1|@$2|3|4|5|6|7|8|H|9|@]|A|@]|B|$]]|$2|C|4|D|6|E|8|I|9|@]|A|@]|B|$F|G]]]]

It's quite simple...

<pre><code>if ($('.mydivclass').length &gt; 0) {
 //do something
}
</code></pre>

entityMap|blocks|key|5st04|text|很简单..。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|d3d3a|if+($('.mydivclass').length+>+0)+{
++//do+something
}|code-block|syntax|javascript^0|0^^$0|$]|1|@$2|3|4|5|6|7|8|H|9|@]|A|@]|B|$]]|$2|C|4|D|6|E|8|I|9|@]|A|@]|B|$F|G]]]]

entityMap|0|type|LINK|mutability|MUTABLE|data|url|http://api.jquery.com/size/|1|http://api.jquery.com/length/|2|http://jsperf.com/check-if-div-exists/3|blocks|key|5sn0h|text|您可以使用size()，但jQuery建议您使用长度来避免另一个函数调用的开销：|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|bgnh8|$('div.mydivclass').length|code-block|syntax|js|ctimh|所以：|d2r8f|//+since+length+is+zero,+it+evaluates+to+false
if+($('div.mydivclass').length)+{|javascript|78g0i|f5evk|2pol|更新|8235m|选择的答案使用了perf测试，但它有一点缺陷，因为它还包括元素选择作为perf的一部分，这不是这里测试的内容。这是一个更新的性能测试：|e23o3|6r8mb|我的第一次测试表明，属性检索比索引检索更快，尽管我认为它可以忽略不计。我仍然喜欢使用长度，因为对于我来说，它对于代码的意图更有意义，而不是更简洁的条件。^0|5|6|0|0|0|0|0|R|0|0|0|T|1|0|0|0|0|13|2|0^^$0|$1|$2|3|4|5|6|$7|8]]|9|$2|3|4|5|6|$7|A]]|B|$2|3|4|5|6|$7|C]]]|D|@$E|F|G|H|2|I|J|19|K|@$L|1A|M|1B|N|O]]|P|@]|6|$]]|$E|Q|G|R|2|S|J|1C|K|@]|P|@]|6|$T|U]]|$E|V|G|W|2|I|J|1D|K|@]|P|@]|6|$]]|$E|X|G|Y|2|S|J|1E|K|@]|P|@]|6|$T|Z]]|$E|10|G|8|2|I|J|1F|K|@]|P|@$L|1G|M|1H|E|1I]]|6|$]]|$E|11|G|A|2|I|J|1J|K|@]|P|@$L|1K|M|1L|E|1M]]|6|$]]|$E|12|G|13|2|I|J|1N|K|@]|P|@]|6|$]]|$E|14|G|15|2|I|J|1O|K|@]|P|@]|6|$]]|$E|16|G|C|2|I|J|1P|K|@]|P|@$L|1Q|M|1R|E|1S]]|6|$]]|$E|17|G|18|2|I|J|1T|K|@]|P|@]|6|$]]]]

You can use <code>size()</code>, but jQuery recommends you use length to avoid the overhead of another function call:

<pre><code>$('div.mydivclass').length
</code></pre>

So:

<pre><code>// since length is zero, it evaluates to false
if ($('div.mydivclass').length) {
</code></pre>

<a href="http://api.jquery.com/size/" rel="noreferrer">http://api.jquery.com/size/</a>

<a href="http://api.jquery.com/length/" rel="noreferrer">http://api.jquery.com/length/</a>

UPDATE

The selected answer uses a perf test, but it's slightly flawed since it is also including element selection as part of the perf, which is not what's being tested here. Here is an updated perf test:

<a href="http://jsperf.com/check-if-div-exists/3" rel="noreferrer">http://jsperf.com/check-if-div-exists/3</a>

My first run of the test shows that property retrieval is faster than index retrieval, although IMO it's pretty negligible. I still prefer using length as to me it makes more sense as to the intent of the code instead of a more terse condition.

entityMap|blocks|key|8mkvn|text|测试div元素显式：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|fc5o7|if(+$('div.mydivclass').length+){...}^0|2|3|0|0|11^^$0|$]|1|@$2|3|4|5|6|7|8|I|9|@$A|J|B|K|C|D]]|E|@]|F|$]]|$2|G|4|H|6|7|8|L|9|@$A|M|B|N|C|D]]|E|@]|F|$]]]]

To test for <code>div</code> elements explicitly:

<code>if( $('div.mydivclass').length ){...}</code>

entityMap|0|type|LINK|mutability|MUTABLE|data|url|http://jsperf.com/check-if-div-exists|blocks|key|2ddpd|text|您可以通过检查从JQuery返回的第一个对象来简化这一过程，如下所示：|unstyled|depth|inlineStyleRanges|entityRanges|34gg4|if+($(".mydivclass")[0]){
++++//+Do+something+if+class+exists
}+else+{
++++//+Do+something+if+class+does+not+exist
}|code-block|syntax|javascript|7i2v4|在这种情况下，如果在第一个([0])索引，然后假设类存在。|offset|length|style|CODE|1ntbr|编辑2013年4月10日：我已经创建了一个jsperf测试用例here..。^0|0|0|E|3|0|V|4|0^^$0|$1|$2|3|4|5|6|$7|8]]]|9|@$A|B|C|D|2|E|F|V|G|@]|H|@]|6|$]]|$A|I|C|J|2|K|F|W|G|@]|H|@]|6|$L|M]]|$A|N|C|O|2|E|F|X|G|@$P|Y|Q|Z|R|S]]|H|@]|6|$]]|$A|T|C|U|2|E|F|10|G|@]|H|@$P|11|Q|12|A|13]]|6|$]]]]

You can simplify this by checking the first object that is returned from JQuery like so:

<pre><code>if ($(".mydivclass")[0]){
 // Do something if class exists
} else {
 // Do something if class does not exist
}
</code></pre>

In this case if there is a truthy value at the first (<code>[0]</code>) index, then assume class exists.

Edit 04/10/2013: I've created a jsperf test case <a href="http://jsperf.com/check-if-div-exists">here</a>.

entityMap|blocks|key|c32ul|text|$('div').hasClass('mydivclass')//+Returns+true+if+the+class+exist.|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|js^0^^$0|$]|1|@$2|3|4|5|6|7|8|E|9|@]|A|@]|B|$C|D]]]]

<pre><code>$('div').hasClass('mydivclass')// Returns true if the class exist.
</code></pre>

entityMap|0|type|LINK|mutability|MUTABLE|data|url|https://stackoverflow.com/questions/16475704/javascript-check-if-classname-exists|blocks|key|2iek7|text|下面是一个不使用Jquery的解决方案|unstyled|depth|inlineStyleRanges|entityRanges|3bgga|var+hasClass+=+element.classList.contains('class+name+to+search');
//+hasClass+is+boolean
if(hasClass+===+true)
{
+++++//+Class+exists
}|code-block|syntax|javascript|33j8a|参考文献link|offset|length^0|0|0|4|4|0^^$0|$1|$2|3|4|5|6|$7|8]]]|9|@$A|B|C|D|2|E|F|R|G|@]|H|@]|6|$]]|$A|I|C|J|2|K|F|S|G|@]|H|@]|6|$L|M]]|$A|N|C|O|2|E|F|T|G|@]|H|@$P|U|Q|V|A|W]]|6|$]]]]

Here is a solution without using Jquery

<pre><code>var hasClass = element.classList.contains('class name to search');
// hasClass is boolean
if(hasClass === true)
{
 // Class exists
}
</code></pre>

reference <a href="https://stackoverflow.com/questions/16475704/javascript-check-if-classname-exists">link</a>

entityMap|0|type|LINK|mutability|MUTABLE|data|url|http://jsfiddle.net/492j1ga6/|1|http://jsfiddle.net/zzpke98u/|2|https://developer.mozilla.org/en-US/docs/Web/API/Node.contains|3|http://jsfiddle.net/qzt1h9m3/|blocks|key|7p48m|text|没有jQuery：|unstyled|depth|inlineStyleRanges|entityRanges|6aqn7|原生JavaScript总是会更快。在这种情况下：(example)|offset|length|rc9g|if+(document.querySelector('.mydivclass')+!==+null)+{
++++//+..+it+exists
}|code-block|syntax|javascript|7ucr2|如果要检查父元素是否包含具有特定类的另一个元素，可以使用以下任一方法。(example)|6gvaq|var+parent+=+document.querySelector('.parent');

if+(parent.querySelector('.child')+!==+null)+{
++++//+..+it+exists+as+a+child
}|cjdfn|或者，您可以使用.contains()方法。(example)|style|CODE|f57hp|var+parent+=+document.querySelector('.parent'),
++++child+=+document.querySelector('.child');

if+(parent.contains(child))+{
++++//+..+it+exists+as+a+child
}|5ml0c|..and最后，如果您想检查给定的元素是否只包含某个类，请使用：|7o88d|if+(el.classList.contains(className))+{
++++//+..+el+contains+the+class
}^0|0|P|9|0|0|0|Z|9|1|0|0|8|B|8|B|2|M|9|3|0|0|0^^$0|$1|$2|3|4|5|6|$7|8]]|9|$2|3|4|5|6|$7|A]]|B|$2|3|4|5|6|$7|C]]|D|$2|3|4|5|6|$7|E]]]|F|@$G|H|I|J|2|K|L|1B|M|@]|N|@]|6|$]]|$G|O|I|P|2|K|L|1C|M|@]|N|@$Q|1D|R|1E|G|1F]]|6|$]]|$G|S|I|T|2|U|L|1G|M|@]|N|@]|6|$V|W]]|$G|X|I|Y|2|K|L|1H|M|@]|N|@$Q|1I|R|1J|G|1K]]|6|$]]|$G|Z|I|10|2|U|L|1L|M|@]|N|@]|6|$V|W]]|$G|11|I|12|2|K|L|1M|M|@$Q|1N|R|1O|13|14]]|N|@$Q|1P|R|1Q|G|1R]|$Q|1S|R|1T|G|1U]]|6|$]]|$G|15|I|16|2|U|L|1V|M|@]|N|@]|6|$V|W]]|$G|17|I|18|2|K|L|1W|M|@]|N|@]|6|$]]|$G|19|I|1A|2|U|L|1X|M|@]|N|@]|6|$V|W]]]]

<h2>Without jQuery:</h2>
Native JavaScript is always going to be faster. In this case: <a href="http://jsfiddle.net/492j1ga6/" rel="noreferrer">(example)</a>
<pre><code>if (document.querySelector('.mydivclass') !== null) {
 // .. it exists
}
</code></pre>
<hr />
If you want to check to see if a parent element contains another element with a specific class, you could use either of the following. <a href="http://jsfiddle.net/zzpke98u/" rel="noreferrer">(example)</a>
<pre><code>var parent = document.querySelector('.parent');

if (parent.querySelector('.child') !== null) {
 // .. it exists as a child
}
</code></pre>
Alternatively, you can use the <a href="https://developer.mozilla.org/en-US/docs/Web/API/Node.contains" rel="noreferrer"><code>.contains()</code></a> method on the parent element. <a href="http://jsfiddle.net/qzt1h9m3/" rel="noreferrer">(example)</a>
<pre><code>var parent = document.querySelector('.parent'),
 child = document.querySelector('.child');

if (parent.contains(child)) {
 // .. it exists as a child
}
</code></pre>
<hr />
..and finally, if you want to check to see if a given element merely contains a certain class, use:
<pre><code>if (el.classList.contains(className)) {
 // .. el contains the class
}
</code></pre>

entityMap|blocks|key|5qr2q|text|简单的代码如下：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|eo612|if+($('.mydivclass').length+>+0)+{
+++//Things+to+do+if+class+exist
}|code-block|syntax|javascript|9n6r3|要隐藏具有特定id的div，请执行以下操作：|1mudp|if+($('#'%2Bgiven_id%2B'.mydivclass').length+>+0)+{
+++//Things+to+do+if+class+exist
}^0|0|0|0^^$0|$]|1|@$2|3|4|5|6|7|8|L|9|@]|A|@]|B|$]]|$2|C|4|D|6|E|8|M|9|@]|A|@]|B|$F|G]]|$2|H|4|I|6|7|8|N|9|@]|A|@]|B|$]]|$2|J|4|K|6|E|8|O|9|@]|A|@]|B|$F|G]]]]

The simple code is given below :

<pre><code>if ($('.mydivclass').length &gt; 0) {
 //Things to do if class exist
}
</code></pre>

To hide the div with particuler id :

<pre><code>if ($('#'+given_id+'.mydivclass').length &gt; 0) {
 //Things to do if class exist
}
</code></pre>

entityMap|blocks|key|f1nst|text|if($(".myClass")[0]+!=+undefined){
++//+it+exists
}else{
++//+does+not+exist
}|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript^0^^$0|$]|1|@$2|3|4|5|6|7|8|E|9|@]|A|@]|B|$C|D]]]]

<pre><code>if($(".myClass")[0] != undefined){
 // it exists
}else{
 // does not exist
}
</code></pre>

entityMap|blocks|key|6gkcj|text|以下是一些方法：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|8nja4|1.++if($("div").hasClass("mydivclass")){
++++//Your+code

++++//It+returns+true+if+any+div+has+'mydivclass'+name.+It+is+a+based+on+the+class+name
++++}

2.+if($("#myid1").hasClass("mydivclass")){
++++//Your+code


++++//++It+returns+true+if+specific+div(myid1)+has+this+class+"mydivclass"+name.+
++++//++It+is+a++based+on+the+specific+div+id's.
++++}+++++++++++
3.+if($("div[class='mydivclass']").length+>+0){
++++//Your+code

+++//+It+returns+all+the+divs+whose+class+name+is+"mydivclass"
+++//++and+it's+length+would+be+greater+than+one.
++++}|code-block|syntax|javascript|1g05j|我们可以根据需要使用上面定义的任何一种方法。^0|0|0^^$0|$]|1|@$2|3|4|5|6|7|8|J|9|@]|A|@]|B|$]]|$2|C|4|D|6|E|8|K|9|@]|A|@]|B|$F|G]]|$2|H|4|I|6|7|8|L|9|@]|A|@]|B|$]]]]

Here are some ways:

<pre><code>1. if($("div").hasClass("mydivclass")){
 //Your code

 //It returns true if any div has 'mydivclass' name. It is a based on the class name
 }

2. if($("#myid1").hasClass("mydivclass")){
 //Your code


 // It returns true if specific div(myid1) has this class "mydivclass" name. 
 // It is a based on the specific div id's.
 } 
3. if($("div[class='mydivclass']").length &gt; 0){
 //Your code

 // It returns all the divs whose class name is "mydivclass"
 // and it's length would be greater than one.
 }
</code></pre>

We can use any one of the abobe defined ways based on the requirement.

entityMap|blocks|key|571c3|text|Javascript中的最佳方式：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|386k4|if+(document.getElementsByClassName("search-box").length+>+0)+{
//+do+something
}|code-block|syntax|javascript^0|0^^$0|$]|1|@$2|3|4|5|6|7|8|H|9|@]|A|@]|B|$]]|$2|C|4|D|6|E|8|I|9|@]|A|@]|B|$F|G]]]]

The best way in Javascript: 

<pre><code>if (document.getElementsByClassName("search-box").length &gt; 0) {
// do something
}
</code></pre>

entityMap|blocks|key|u4cl|text|var+x+=+document.getElementsByClassName("class+name");
if+(x[0])+{
alert('has');
}+else+{
alert('no+has');
}|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript^0^^$0|$]|1|@$2|3|4|5|6|7|8|E|9|@]|A|@]|B|$C|D]]]]

<pre><code>var x = document.getElementsByClassName("class name");
if (x[0]) {
alert('has');
} else {
alert('no has');
}
</code></pre>

entityMap|blocks|key|ej90m|text|在Jquery中，您可以这样使用。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3jefd|if+($(".className")[0]){

+++//+Do+something+if+class+exists

}+else+{

//+Do+something+if+class+does+not+exist

}|code-block|syntax|javascript|dgi3h|使用JavaScript|8btpp|if+(document.getElementsByClassName("className").length+>+0)+{

//+Do+something+if+class+exists

}else{

++++//+Do+something+if+class+does+not+exist......

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

In Jquery you can use like this.
<pre><code>if ($(&quot;.className&quot;)[0]){

 // Do something if class exists

} else {

// Do something if class does not exist

}
</code></pre>
With JavaScript
<pre><code>if (document.getElementsByClassName(&quot;className&quot;).length &gt; 0) {

// Do something if class exists

}else{

 // Do something if class does not exist......

}
</code></pre>

entityMap|blocks|key|9drcj|text|if+($("#myid1").hasClass("mydivclass")){//+Do+any+thing}|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|js^0^^$0|$]|1|@$2|3|4|5|6|7|8|E|9|@]|A|@]|B|$C|D]]]]

<pre><code>if ($(&quot;#myid1&quot;).hasClass(&quot;mydivclass&quot;)){// Do any thing}
</code></pre>

entityMap|blocks|key|6bfa1|text|使用此选项可搜索整个页面|type|unstyled|depth|inlineStyleRanges|entityRanges|data|ahcn2|if($('*').hasClass('mydivclass')){
//+Do+Stuff
}|code-block|syntax|javascript^0|0^^$0|$]|1|@$2|3|4|5|6|7|8|H|9|@]|A|@]|B|$]]|$2|C|4|D|6|E|8|I|9|@]|A|@]|B|$F|G]]]]

Use this to search whole page

<pre><code>if($('*').hasClass('mydivclass')){
// Do Stuff
}
</code></pre>

entityMap|blocks|key|d4lec|text|下面是Javascript中check类(hasClass)的示例解决方案：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|75n7a|const+mydivclass+=+document.querySelector('.mydivclass');
//+if+'hasClass'+is+exist+on+'mydivclass'
if(mydivclass.classList.contains('hasClass'))+{
+++//+do+something+if+'hasClass'+is+exist.
}|code-block|syntax|javascript^0|0^^$0|$]|1|@$2|3|4|5|6|7|8|H|9|@]|A|@]|B|$]]|$2|C|4|D|6|E|8|I|9|@]|A|@]|B|$F|G]]]]

Here is very sample solution for check class (hasClass) in Javascript:

<pre class="lang-js prettyprint-override"><code>const mydivclass = document.querySelector('.mydivclass');
// if 'hasClass' is exist on 'mydivclass'
if(mydivclass.classList.contains('hasClass')) {
 // do something if 'hasClass' is exist.
}
</code></pre>

Using jQuery I'm programmatically generating a bunch of <code>div</code>'s like this:

<pre><code>&lt;div class="mydivclass" id="myid1"&gt;Some Text1&lt;/div&gt;
&lt;div class="mydivclass" id="myid2"&gt;Some Text2&lt;/div&gt;
</code></pre>

Somewhere else in my code I need to detect if these DIVs exist. The class name for the divs is the same but the ID changes for each div. Any idea how to detect them using jQuery?

jQuery: Check if div with certain class name exists

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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 使用jQuery，我以编程方式生成了一堆div是这样的： Some Text1Some Text2 在我的代码中的其他地方，我需要检测这些DIVs是否存在。div的类名是相同的，但每个div的ID都不同。你知道怎么用jQuery检测它们吗？

问jQuery:检查是否存在具有特定类名的div
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