jQuery: Check if div with certain class name exists

问题

Using jQuery I\'m programmatically generating a bunch of div\'s like this:

<div class=\"mydivclass\" id=\"myid1\">Some Text1</div>
<div class=\"mydivclass\" id=\"myid2\">Some Text2</div>

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?

回答1:

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

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

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

Edit 04/10/2013: I've created a jsperf test case here.

回答2:

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

$('div.mydivclass').length

So:

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

http://api.jquery.com/size/

http://api.jquery.com/length/

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:

http://jsperf.com/check-if-div-exists/3

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.

回答3:

Without jQuery:

Native JavaScript is always going to be faster. In this case: (example)

if (document.querySelector('.mydivclass') !== null) {
    // .. it exists
}

---

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. (example)

var parent = document.querySelector('.parent');

if (parent.querySelector('.child') !== null) {
    // .. it exists as a child
}

Alternatively, you can use the .contains() method on the parent element. (example)

var parent = document.querySelector('.parent'),
    child = document.querySelector('.child');

if (parent.contains(child)) {
    // .. it exists as a child
}

---

..and finally, if you want to check to see if a given element merely contains a certain class, use:

if (el.classList.contains(className)) {
    // .. el contains the class
}

回答4:

$('div').hasClass('mydivclass')// Returns true if the class exist.

回答5:

Here is a solution without using Jquery

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

reference link

回答6:

It's quite simple...

if ($('.mydivclass').length > 0) {
  //do something
}

回答7:

To test for div elements explicitly:

if( $('div.mydivclass').length ){...}

回答8:

The simple code is given below :

if ($('.mydivclass').length > 0) {
   //Things to do if class exist
}

To hide the div with particuler id :

if ($('#'+given_id+'.mydivclass').length > 0) {
   //Things to do if class exist
}

回答9:

Here are some ways:

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.
    }

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

回答10:

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

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

回答11:

check if the div exists with a certain class

if ($(".mydivclass").length > 0) //it exists 
{

}

回答12:

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

回答13:

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

回答14:

The best way in Javascript:

if (document.getElementsByClassName("search-box").length > 0) {
// do something
}

回答15:

In Jquery you can use like this.

if ($(".className")[0]){

   // Do something if class exists

} else {

// Do something if class does not exist

}

With JavaScript

if (document.getElementsByClassName("className").length > 0) {

// Do something if class exists

}else{

    // Do something if class does not exist

}

回答16:

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

const mydivclass = document.querySelector('.mydivclass');
// if 'hasClass' is exist on 'mydivclass'
if(mydivclass.classList.contains('hasClass')) {
   // do something if 'hasClass' is exist.
}

回答17:

Use this to search whole page

if($('*').hasClass('mydivclass')){
// Do Stuff
}

回答18:

if($("#myid1").hasClass("mydivclass")){//Do any thing}

来源：https://stackoverflow.com/questions/5783280/jquery-check-if-div-with-certain-class-name-exists