How to add a class to a given element?

Question

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?

Yeomanry

To anyone reading this thread in 2020 or later, skip the old className method and use element.classList.add("my-class") instead. – Scandent

Answer 1

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.

Shari

If the only work on the whole page that needs to be done with JavaScript is this class name addition, then yes. But I can't see this being the only dynamic part of the page. A library will help with everything else as well. At 30-50kb jQuery is hardly a hit worth discussing. – Verst

"A library will help with everything else as well" - apart from learning JavaScript – Exult

What does adding a class to a DOM element have to do with learning the language? document.getElementById('div1').className is as much a library related issue as using jQuery to do the same is. The question was "how can I do that", a thoroughly tested library is the sensible answer. – Verst

@thenduks: I'm sure you know that JavaScript !== jQuery. It's a good thing that the answers to this question include library and non library solutions because it is important to know how things work not just the simplest way to accomplish them. You'll notice this question is tagged javascript – Exult

@meouw: I agree with you. jQuery is written in JavaScript, however, so I maintain that mentioning to the OP that a library is a good idea is not 'pushing a framework down [his] throat'. That's all. – Verst

how to remove this class? is there any method to do this in javaScript,not with jQuery – Paraplegia

@QadirHussain: You have to parse the string manually and then assign it to className. – Clipped

how to do in javascript with multiple elements? – Cythera

adding a class like so doesnt trigger transitions for me.. is this a known issue or? – Vaccaro

It's important to note that using this method will add the class as many times as the line d.className += " otherclass" is called. That may or may not be the desired outcome. Check out the second most voted answer for adding a class only once. – Esta

And don't forget that leading space! ;) – Mercado

Downvoted, not because it is a bad answer, but there is a better way nowadays using element.classList.add as discussed in this answer – Campfire

Unless your job requires it specifically, please don't support IE9 and lower :) – Tragicomedy

@Verst Your thoroughly tested library is a way to avoid a sensible answer. – Flintlock

Answer 2

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.

Chou

It's a shame that this isn't supported prior to IE 10.0 because it's an excellent feature and the easiest solution to an issue I come across often. – Jitney

A polyfill for classList is available. – Recycle

element.classList docs on MDN. – Redden

what about element.classList[length] = "otherclass"? – Jupon

This one seems to be the best one to use, as the ones with space at least feel like hacks - not ment for adding classes... – Victorious

@SilverRingvee A further risk of the space approach is that some other developer might not know it's vital, and remove it in order to clean things up. – Lovash

In what sense do you need to handle duplicates? In removal? You can use classList.remove(...) in that case, but you can still use className to add. – Comportment

This should be the accepted answer in 2019 and beyond. – Campfire

For multiple classes: element.classList.add("one", "tow", ...); – Brickle

how can we do this with getElementByClassName – Lydell

Answer 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..

Outlaw

And to remove using this method? – Crowson

@Crowson simply set the class back to a single defined name d.className = 'originalClass'; – Fledgling

@Fledgling - if you have more than one class you need to keep (which happens a lot these days), that will not work. – Wilie

To remove the old-fashioned way, split the classname on whitespace, remove the one you don't want from the resulting array, then join the array again... or use element.classList.remove. – Campfire

Answer 4

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")

Colorfast

Wow thanks :) Will the shorthand version (a.classList ? ...) have any speed difference compared to the normal one (if (a.classList) { ....)? – Parvenu

There's olso classList.remove(). Why didn't you used it? it's much faster than jQuery jsperf.com/remove-class-vanilla-vs-jquery – Dincolo

@FezVrasta classList isn't supported before IE 10, which still has a decent market share (+13% on netmarketshare.com). – Arvid

@Arvid he used classList for everything except to remove classes, this is why I'm asking it. – Dincolo

@FezVrasta Under cross compatible I did use .add() but only after checking to see if it is available, hense cross compatible. For remove I did not bother to repeat myself so I did not include as many options. – Colorfast

Isn't a.className = a.className + c; adding the class back? I don't get it. – Globular

And it looks like DOMTokenList has a remove method too. – Globular

Answer 5

2 different ways to add class using JavaScript

JavaScript provides 2 different ways by which you can add classes to HTML elements:

1. Using element.classList.add() Method
2. Using className property

Using both methods you can add single or multiple classes at once.

1. Using element.classList.add() Method

var element = document.querySelector('.box');
// using add method
// adding single class
element.classList.add('color');

// adding multiple class
element.classList.add('border', 'shadow');

.box {
    width: 200px;
    height: 100px;
}
.color {
    background: skyblue;
}
.border {
    border: 2px solid black;
}
.shadow {
    box-shadow: 5px 5px 5px gray;
}

<div class="box">My Box</div>

2. Using element.className Property

Note: Always use += operator and add a space before class name to add class with classList method.

var element = document.querySelector('.box');
// using className Property
// adding single class
element.className += ' color';

// adding multiple class
// keep classes space separated
element.className += ' border shadow';

.box {
    width: 200px;
    height: 100px;
}
.color {
    background: skyblue;
}
.border {
    border: 2px solid black;
}
.shadow {
    box-shadow: 5px 5px 5px gray;
}

<div class="box">My Box</div>

Perfect

plus one for adding more than one class. – Diseur

Answer 6

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");

Rubinrubina

That's already been answered several times by other users, including discussions of browser support and shims. – Leveloff

@Leveloff I didn't see that previous answer was given and its my mistake. You can flag this answer – Rubinrubina

@ShoaibChikate: you can also delete the answer if you'd like (you'll keep the points). Just trying to reduce clutter on this question; totally up to you. – Platyhelminth

Answer 7

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')

Smite

Answer 8

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;
}

Exult

if( cn.indexOf( classname ) != -1 ) { return; } Beware that if you add the class “btn” with the class “btn-info” being already here, this fails. – Peart

you should use element.className.split(" "); to prevent the problem @AlexandreDieulot reported here. – Effluence

Answer 9

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.

Verst

Answer 10

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")

Interdental

very nice, but not supported in IE <= 9 or Safari <=5.0 ... :( (caniuse.com/classlist) – Richmond

This has already been discussed, including browser support. – Platyhelminth

Answer 11

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.)

Bookstand

Answer 12

This might be helpful for WordPress developers etc.

document.querySelector('[data-section="section-hb-button-1"] .ast-custom-button').classList.add('TryMyClass');

Paracelsus

Answer 13

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);
}

Keelykeen

Answer 14

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
	})
}

Studnia

Answer 15

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');

Hurd

Answer 16

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>

Clientele

how about to target the last class instead? – Plossl

Answer 17

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');

Degraw

Answer 18

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.

Autodidact

Answer 19

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)
  }
}

Dripstone

Answer 20

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";
})

Scherle

Answer 21

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()

Architectonic

Answer 22

The majority of people use a .classList.add on a getElementById, but I i wanted to use it on a getElementByClassName. To do that, i was using a forEach like this :

document.getElementsByClassName("class-name").forEach(element => element.classList.add("new-class"));

But it didn't work because i discovered that getElementsByClassName returns a HTML collection and not an array. To handle that I converted it to an array with this code :

[...document.getElementsByClassName("class-name")].forEach(element => element.classList.add("new-class"));

Dispensable

Answer 23

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>

Redfield

Answer 24

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');

Darvon

This has already been discussed, along with browser support. – Platyhelminth

Answer 25

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.

Shrum

Answer 26

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>

Petunia

it will replace the class not append ! Maybe be a line is missing or a oldClass+" "+classToAppend instead of the last classToAppend – Ascarid

indexOf is a naive solution and has a problem already pointed out. – Platyhelminth

Answer 27

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

Covell

Answer 28

In YUI, if you include yuidom, you can use

YAHOO.util.Dom.addClass('div1','className');

HTH

Osmium

It said JavaScript, not jQuery or YUI. – Airplane