How to add a class to a given element?

I have an element that already has a class:

<div class="someclass">
    <img ... id="image1" name="image1" />
</div>

Now, I want to create a JavaScript function that will add a class to the div (not replace, but add).

How can I do that?

61 thoughts on “How to add a class to a given element?”

  1. first, give the div an id. Then, call function appendClass:

    <script language="javascript">
      function appendClass(elementId, classToAppend){
        var oldClass = document.getElementById(elementId).getAttribute("class");
        if (oldClass.indexOf(classToAdd) == -1)
        {
          document.getElementById(elementId).setAttribute("class", classToAppend);
        }
    }
    </script>
    
    Reply
  2. Assuming you’re doing more than just adding this one class (eg, you’ve got asynchronous requests and so on going on as well), I’d recommend a library like Prototype or jQuery.

    This will make just about everything you’ll need to do (including this) very simple.

    So let’s say you’ve got jQuery on your page now, you could use code like this to add a class name to an element (on load, in this case):

    $(document).ready( function() {
      $('#div1').addClass( 'some_other_class' );
    } );
    

    Check out the jQuery API browser for other stuff.

    Reply
  3. find your target element “d” however you wish and then:

    d.className += ' additionalClass'; //note the space
    

    you can wrap that in cleverer ways to check pre-existence, and check for space requirements etc..

    Reply
  4. Just to elaborate on what others have said, multiple CSS classes are combined in a single string, delimited by spaces. Thus, if you wanted to hard-code it, it would simply look like this:

    <div class="someClass otherClass yetAnotherClass">
          <img ... id="image1" name="image1" />
    </div>
    

    From there you can easily derive the javascript necessary to add a new class… just append a space followed by the new class to the element’s className property. Knowing this, you can also write a function to remove a class later should the need arise.

    Reply
  5. When the work I’m doing doesn’t warrant using a library, I use these two functions:

    function addClass( classname, element ) {
        var cn = element.className;
        //test for existance
        if( cn.indexOf( classname ) != -1 ) {
            return;
        }
        //add a space if the element already has class
        if( cn != '' ) {
            classname = ' '+classname;
        }
        element.className = cn+classname;
    }
    
    function removeClass( classname, element ) {
        var cn = element.className;
        var rxp = new RegExp( "\\s?\\b"+classname+"\\b", "g" );
        cn = cn.replace( rxp, '' );
        element.className = cn;
    }
    
    Reply
  6. You can use the classList.add OR classList.remove method to add/remove a class from a element.

    var nameElem = document.getElementById("name")
    nameElem.classList.add("anyclss")
    

    The above code will add(and NOT replace) a class “anyclass” to nameElem.
    Similarly you can use classList.remove() method to remove a class.

    nameElem.classList.remove("anyclss")
    
    Reply
  7. The easiest way to do this without any framework is to use element.classList.add method.

    var element = document.getElementById("div1");
    element.classList.add("otherclass");
    

    Edit:
    And if you want to remove class from an element –

    element.classList.remove("otherclass");
    

    I prefer not having to add any empty space and duplicate entry handling myself (which is required when using the document.className approach). There are some browser limitations, but you can work around them using polyfills.

    Reply
  8. Another approach to add the class to element using pure JavaScript

    For adding class:

    document.getElementById("div1").classList.add("classToBeAdded");
    

    For removing class:

    document.getElementById("div1").classList.remove("classToBeRemoved");
    
    Reply
  9. This js code works for me

    provides classname replacement

    var DDCdiv = hEle.getElementBy.....
    
    var cssCNs = DDCdiv.getAttribute('class');
    var Ta = cssCNs.split(' '); //split into an array
    for (var i=0; i< Ta.length;i++)
    {
        if (Ta[i] == 'visible'){
            Ta[i] = 'hidden';
            break;// quit for loop
        }
        else if (Ta[i] == 'hidden'){
            Ta[i] = 'visible';
        break;// quit for loop
        }
    }
    DDCdiv.setAttribute('class',Ta.join(' ') );  // Join array with space and set class name
    

    To add just use

    var cssCNs = DDCdiv.getAttribute('class');
    var Ta = cssCNs.split(' '); //split into an array
    Ta.push('New class name');
    // Ta.push('Another class name');//etc...
    DDCdiv.setAttribute('class',Ta.join(' ') );  // Join array with space and set class name
    

    To remove use

    var cssCNs = DDCdiv.getAttribute('class');
    var Ta = cssCNs.split(' '); //split into an array
    
    for (var i=0; i< Ta.length;i++)
    {
        if (Ta[i] == 'visible'){
            Ta.splice( i, 1 );
            break;// quit for loop
        }
    }
    DDCdiv.setAttribute('class',Ta.join(' ') );  // Join array with space and set class name
    

    Hope this is helpful to sombody

    Reply
  10. To add, remove or check element classes in a simple way:

    var uclass = {
        exists: function(elem,className){var p = new RegExp('(^| )'+className+'( |$)');return (elem.className && elem.className.match(p));},
        add: function(elem,className){if(uclass.exists(elem,className)){return true;}elem.className += ' '+className;},
        remove: function(elem,className){var c = elem.className;var p = new RegExp('(^| )'+className+'( |$)');c = c.replace(p,' ').replace(/  /g,' ');elem.className = c;}
    };
    
    var elem = document.getElementById('someElem');
    //Add a class, only if not exists yet.
    uclass.add(elem,'someClass');
    //Remove class
    uclass.remove(elem,'someClass');
    
    Reply
  11. You can use the API querySelector to select your element and then create a function with the element and the new classname as parameters. Using classlist for modern browsers, else for IE8. Then you can call the function after an event.

     //select the dom element
     var addClassVar = document.querySelector('.someclass');
    
     //define the addclass function
     var addClass = function(el,className){
       if (el.classList){
         el.classList.add(className);
       }
       else {
         el.className += ' ' + className;
      }
    };
    
    //call the function
    addClass(addClassVar, 'newClass');
    
    Reply
  12. I think it’s better to use pure JavaScript, which we can run on the DOM of the Browser.

    Here is the functional way to use it. I have used ES6 but feel free to use ES5 and function expression or function definition, whichever suits your JavaScript StyleGuide.

    'use strict'
    
    const oldAdd = (element, className) => {
      let classes = element.className.split(' ')
      if (classes.indexOf(className) < 0) {
        classes.push(className)
      }
      element.className = classes.join(' ')
    }
    
    const oldRemove = (element, className) => {
      let classes = element.className.split(' ')
      const idx = classes.indexOf(className)
      if (idx > -1) {
        classes.splice(idx, 1)
      }
      element.className = classes.join(' ')
    }
    
    const addClass = (element, className) => {
      if (element.classList) {
        element.classList.add(className)
      } else {
        oldAdd(element, className)
      }
    }
    
    const removeClass = (element, className) => {
      if (element.classList) {
        element.classList.remove(className)
      } else {
        oldRemove(element, className)
      }
    }
    Reply
  13. Add Class

    • Cross Compatible

      In the following example we add a classname to the <body> element. This is IE-8 compatible.

      var a = document.body;
      a.classList ? a.classList.add('classname') : a.className += ' classname';
      

      This is shorthand for the following..

      var a = document.body;
      if (a.classList) {
          a.classList.add('wait');
      } else {
          a.className += ' wait';
      }
      

    • Performance

      If your more concerned with performance over cross-compatibility you can shorten it to the following which is 4% faster.

      var z = document.body;
      document.body.classList.add('wait');
      

    • Convenience

      Alternatively you could use jQuery but the resulting performance is significantly slower. 94% slower according to jsPerf

      $('body').addClass('wait');
      


    Removing the class

    • Performance

      Using jQuery selectively is the best method for removing a class if your concerned with performance

      var a = document.body, c = ' classname';
      $(a).removeClass(c);
      

    • Without jQuery it’s 32% slower

      var a = document.body, c = ' classname';
      a.className = a.className.replace( c, '' );
      a.className = a.className + c;
      

    References

    1. jsPerf Test Case: Adding a Class
    2. jsPerf Test Case: Removing a Class

    Using Prototype

    Element("document.body").ClassNames.add("classname")
    Element("document.body").ClassNames.remove("classname")
    Element("document.body").ClassNames.set("classname")
    

    Using YUI

    YAHOO.util.Dom.hasClass(document.body,"classname")
    YAHOO.util.Dom.addClass(document.body,"classname")
    YAHOO.util.Dom.removeClass(document.body,"classname")
    
    Reply
  14. To add an additional class to an element:

    To add a class to an element, without removing/affecting existing values, append a space and the new classname, like so:

    document.getElementById("MyElement").className += " MyClass";
    

    To change all classes for an element:

    To replace all existing classes with one or more new classes, set the className attribute:

    document.getElementById("MyElement").className = "MyClass";
    

    (You can use a space-delimited list to apply multiple classes.)

    Reply
  15. If you’re only targeting modern browsers:

    Use element.classList.add to add a class:

    element.classList.add("my-class");
    

    And element.classList.remove to remove a class:

    element.classList.remove("my-class");
    

    If you need to support Internet Explorer 9 or lower:

    Add a space plus the name of your new class to the className property of the element. First, put an id on the element so you can easily get a reference.

    <div id="div1" class="someclass">
        <img ... id="image1" name="image1" />
    </div>
    

    Then

    var d = document.getElementById("div1");
    d.className += " otherclass";
    

    Note the space before otherclass. It’s important to include the space otherwise it compromises existing classes that come before it in the class list.

    See also element.className on MDN.

    Reply
  16. If you don’t want to use jQuery and want to support older browsers:

    function addClass(elem, clazz) {
        if (!elemHasClass(elem, clazz)) {
            elem.className += " " + clazz;
        }
    }
    
    function elemHasClass(elem, clazz) {
        return new RegExp("( |^)" + clazz + "( |$)").test(elem.className);
    }
    
    Reply
  17. Sample with pure JS. In first example we get our element’s id and add e.g. 2 classes.

    document.addEventListener('DOMContentLoaded', function() {
        document.getElementsById('tabGroup').className = "anyClass1 anyClass2";
    })
    

    In second example we get element’s class name and add 1 more.

    document.addEventListener('DOMContentLoaded', function() {
        document.getElementsByClassName('tabGroup')[0].className = "tabGroup ready";
    })
    
    Reply
  18. I know IE9 is shutdown officially and we can achieve it with element.classList as many told above but I just tried to learn how it works without classList with help of many answers above I could learn it.

    Below code extends many answers above and improves them by avoiding adding duplicate classes.

    function addClass(element,className){
      var classArray = className.split(' ');
      classArray.forEach(function (className) {
        if(!hasClass(element,className)){
          element.className += " "+className;
        }
      });            
    }
    //this will add 5 only once
    addClass(document.querySelector('#getbyid'),'3 4 5 5 5');
    
    Reply
  19. Shortest

    image1.parentNode.className+=' box';
    
    image1.parentNode.className+=' box';
    .box { width: 100px; height:100px; background: red; }
    <div class="someclass">
        <img ... id="image1" name="image1" />
    </div>
    Reply
  20. I too think that the fastest way is to use Element.prototype.classList as in es5: document.querySelector(".my.super-class").classList.add('new-class')
    but in ie8 there is no such thing as Element.prototype.classList, anyway you can polyfill it with this snippet (fell free to edit and improve it):

    if(Element.prototype.classList === void 0){
    	function DOMTokenList(classes, self){
    		typeof classes == "string" && (classes = classes.split(' '))
    		while(this.length){
    			Array.prototype.pop.apply(this);
    		}
    		Array.prototype.push.apply(this, classes);
    		this.__self__ = this.__self__ || self
    	}
    
    	DOMTokenList.prototype.item = function (index){
    		return this[index];
    	}
    
    	DOMTokenList.prototype.contains = function (myClass){
    		for(var i = this.length - 1; i >= 0 ; i--){
    			if(this[i] === myClass){
    				return true;
    			}
    		}
    		return false
    	}
    
    	DOMTokenList.prototype.add = function (newClass){
    		if(this.contains(newClass)){
    			return;
    		}
    		this.__self__.className += (this.__self__.className?" ":"")+newClass;
    		DOMTokenList.call(this, this.__self__.className)
    	}
    
    	DOMTokenList.prototype.remove = function (oldClass){
    		if(!this.contains(newClass)){
    			return;
    		}
    		this[this.indexOf(oldClass)] = undefined
    		this.__self__.className = this.join(' ').replace(/  +/, ' ')
    		DOMTokenList.call(this, this.__self__.className)
    	}
    
    	DOMTokenList.prototype.toggle = function (aClass){
    		this[this.contains(aClass)? 'remove' : 'add'](aClass)
    		return this.contains(aClass);
    	}
    
    	DOMTokenList.prototype.replace = function (oldClass, newClass){
    		this.contains(oldClass) && this.remove(oldClass) && this.add(newClass)
    	}
    
    	Object.defineProperty(Element.prototype, 'classList', {
    		get: function() {
    			return new DOMTokenList( this.className, this );
    		},
    		enumerable: false
    	})
    }
    Reply
  21. In my case, I had more than one class called main-wrapper in the DOM, but I only wanted to affect the parent main-wrapper. Using :first Selector (https://api.jquery.com/first-selector/), I could select the first matched DOM element. This was the solution for me:

    $(document).ready( function() {
        $('.main-wrapper:first').addClass('homepage-redesign');
        $('#deals-index > div:eq(0) > div:eq(1)').addClass('doubleheaderredesign');
    } );
    

    I also did the same thing for the second children of a specific div in my DOM as you can see in the code where I used $('#deals-index > div:eq(0) > div:eq(1)').addClass('doubleheaderredesign');.

    NOTE: I used jQuery as you can see.

    Reply
  22. For those using Lodash and wanting to update className string:

    // get element reference
    var elem = document.getElementById('myElement');
    
    // add some classes. Eg. 'nav' and 'nav header'
    elem.className = _.chain(elem.className).split(/[\s]+/).union(['nav','navHeader']).join(' ').value()
    
    // remove the added classes
    elem.className = _.chain(elem.className).split(/[\s]+/).difference(['nav','navHeader']).join(' ').value()
    
    Reply
  23. document.getElementById('some_id').className+='  someclassname'
    

    OR:

    document.getElementById('some_id').classList.add('someclassname')
    

    First approach helped in adding the class when second approach didn’t work.
    Don’t forget to keep a space in front of the ' someclassname' in the first approach.

    For removal you can use:

    document.getElementById('some_id').classList.remove('someclassname')
    
    Reply
  24. You can use modern approach similar to jQuery

    If you need to change only one element, first one that JS will find in DOM, you can use this:

    document.querySelector('.someclass').className += " red";
    .red {
      color: red;
    }
    <div class="someclass">
      <p>This method will add class "red" only to first element in DOM</p>
    </div>
    
    <div class="someclass">
      <p>lorem ipsum</p>
    </div>
    
    <div class="someclass">
      <p>lorem ipsum</p>
    </div>
    
    <div class="someclass">
      <p>lorem ipsum</p>
    </div>

    Keep in mind to leave one space before class name.

    If you have multiple classes where you want to add new class, you can use it like this

    document.querySelectorAll('.someclass').forEach(function(element) {
      element.className += " red";
    });
    .red {
      color: red;
    }
    <div class="someclass">
      <p>This method will add class "red" to all elements in DOM that have "someclass" class.</p>
    </div>
    
    <div class="someclass">
      <p>lorem ipsum</p>
    </div>
    
    <div class="someclass">
      <p>lorem ipsum</p>
    </div>
    
    <div class="someclass">
      <p>lorem ipsum</p>
    </div>
    Reply

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