How can I change an element's class with JavaScript?


How can I change a class of an HTML element in response to an onclick event using JavaScript?


THE OPTIONS.

Here is a little style vs. classList examples to get you to see what are the options you have available and how to use classList to do what you want.

style vs. classList

The difference between style and classList is that with style you're adding to the style properties of the element, but classList is kinda controlling the class(es) of the element (add, remove, toggle, contain), I will show you how to use the add and remove method since those are the popular ones.


Style Example

If you want to add margin-top property into an element, you would do in such:

// Get the Element
const el = document.querySelector('#element');

// Add CSS property 
el.style.margintop = "0px"
el.style.margintop = "25px" // This would add a 25px to the top of the element.

classList Example

Let say we have a <div class="class-a class-b">, in this case, we have 2 classes added to our div element already, class-a and class-b, and we want to control what classes remove and what class to add. This is where classList becomes handy.

Remove class-b

// Get the Element
const el = document.querySelector('#element');

// Remove class-b style from the element
el.classList.remove("class-b")

Add class-c

// Get the Element
const el = document.querySelector('#element');

// Add class-b style from the element
el.classList.add("class-c")



Modern HTML5 Techniques for changing classes

Modern browsers have added classList which provides methods to make it easier to manipulate classes without needing a library:

document.getElementById("MyElement").classList.add('MyClass');

document.getElementById("MyElement").classList.remove('MyClass');

if ( document.getElementById("MyElement").classList.contains('MyClass') )

document.getElementById("MyElement").classList.toggle('MyClass');

Unfortunately, these do not work in Internet Explorer prior to v10, though there is a shim to add support for it to IE8 and IE9, available from this page. It is, though, getting more and more supported.

Simple cross-browser solution

The standard JavaScript way to select an element is using document.getElementById("Id"), which is what the following examples use - you can of course obtain elements in other ways, and in the right situation may simply use this instead - however, going into detail on this is beyond the scope of the answer.

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.)

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 remove a class from an element:

To remove a single class to an element, without affecting other potential classes, a simple regex replace is required:

document.getElementById("MyElement").className =
   document.getElementById("MyElement").className.replace
      ( /(?:^|\s)MyClass(?!\S)/g , '' )
/* Code wrapped for readability - above is all one statement */

An explanation of this regex is as follows:

(?:^|\s) # Match the start of the string, or any single whitespace character

MyClass  # The literal text for the classname to remove

(?!\S)   # Negative lookahead to verify the above is the whole classname
         # Ensures there is no non-space character following
         # (i.e. must be end of string or a space)

The g flag tells the replace to repeat as required, in case the class name has been added multiple times.

To check if a class is already applied to an element:

The same regex used above for removing a class can also be used as a check as to whether a particular class exists:

if ( document.getElementById("MyElement").className.match(/(?:^|\s)MyClass(?!\S)/) )


Assigning these actions to onclick events:

Whilst it is possible to write JavaScript directly inside the HTML event attributes (such as onclick="this.className+=' MyClass'") this is not recommended behaviour. Especially on larger applications, more maintainable code is achieved by separating HTML markup from JavaScript interaction logic.

The first step to achieving this is by creating a function, and calling the function in the onclick attribute, for example:

<script type="text/javascript">
    function changeClass(){
        // Code examples from above
    }
</script>
...
<button onclick="changeClass()">My Button</button>

(It is not required to have this code in script tags, this is simply for brevity of example, and including the JavaScript in a distinct file may be more appropriate.)

The second step is to move the onclick event out of the HTML and into JavaScript, for example using addEventListener

<script type="text/javascript">
    function changeClass(){
        // Code examples from above
    }

    window.onload = function(){
        document.getElementById("MyElement").addEventListener( 'click', changeClass);
    }
</script>
...
<button id="MyElement">My Button</button>

(Note that the window.onload part is required so that the contents of that function are executed after the HTML has finished loading - without this, the MyElement might not exist when the JavaScript code is called, so that line would fail.)


JavaScript Frameworks and Libraries

The above code is all in standard JavaScript, however it is common practise to use either a framework or a library to simplify common tasks, as well as benefit from fixed bugs and edge cases that you might not think of when writing your code.

Whilst some people consider it overkill to add a ~50 KB framework for simply changing a class, if you are doing any substantial amount of JavaScript work, or anything that might have unusual cross-browser behaviour, it is well worth considering.

(Very roughly, a library is a set of tools designed for a specific task, whilst a framework generally contains multiple libraries and performs a complete set of duties.)

The examples above have been reproduced below using jQuery, probably the most commonly used JavaScript library (though there are others worth investigating too).

(Note that $ here is the jQuery object.)

Changing Classes with jQuery:

$('#MyElement').addClass('MyClass');

$('#MyElement').removeClass('MyClass');

if ( $('#MyElement').hasClass('MyClass') )

In addition, jQuery provides a shortcut for adding a class if it doesn't apply, or removing a class that does:

$('#MyElement').toggleClass('MyClass');


Assigning a function to a click event with jQuery:

$('#MyElement').click(changeClass);

or, without needing an id:

$(':button:contains(My Button)').click(changeClass);



You could also just do:

document.getElementById('id').classList.add('class');
document.getElementById('id').classList.remove('class');

And to toggle a class (remove if exists else add it):

document.getElementById('id').classList.toggle('class');

In one of my old projects that did not use jQuery, I built the following functions for adding, removing and checking if element has class:

function hasClass(ele, cls) {
    return ele.className.match(new RegExp('(\\s|^)' + cls + '(\\s|$)'));
}
function addClass(ele, cls) {
    if (!hasClass(ele, cls)) ele.className += " " + cls;
}
function removeClass(ele, cls) {
    if (hasClass(ele, cls)) {
        var reg = new RegExp('(\\s|^)' + cls + '(\\s|$)');
        ele.className = ele.className.replace(reg, ' ');
    }
}

So, for example, if I want onclick to add some class to the button I can use this:

<script type="text/javascript">
    function changeClass(btn, cls) {
        if(!hasClass(btn, cls)) {
            addClass(btn, cls);
        }
    }
</script>
...
<button onclick="changeClass(this, "someClass")">My Button</button>

By now for sure it would just be better to use jQuery.


You can use node.className like so:

document.getElementById('foo').className = 'bar';

This should work in IE5.5 and up according to PPK.


Wow, surprised there are so many overkill answers here...

<div class="firstClass" onclick="this.className='secondClass'">

Using pure JavaScript code:

function hasClass(ele, cls) {
    return ele.className.match(new RegExp('(\\s|^)' + cls + '(\\s|$)'));
}

function addClass(ele, cls) {
    if (!this.hasClass(ele, cls)) ele.className += " " + cls;
}

function removeClass(ele, cls) {
    if (hasClass(ele, cls)) {
        var reg = new RegExp('(\\s|^)' + cls + '(\\s|$)');
        ele.className = ele.className.replace(reg, ' ');
    }
}

function replaceClass(ele, oldClass, newClass){
    if(hasClass(ele, oldClass)){
        removeClass(ele, oldClass);
        addClass(ele, newClass);
    }
    return;
}

function toggleClass(ele, cls1, cls2){
    if(hasClass(ele, cls1)){
        replaceClass(ele, cls1, cls2);
    }else if(hasClass(ele, cls2)){
        replaceClass(ele, cls2, cls1);
    }else{
        addClass(ele, cls1);
    }
}

This is working for me:

function setCSS(eleID) {
    var currTabElem = document.getElementById(eleID);

    currTabElem.setAttribute("class", "some_class_name");
    currTabElem.setAttribute("className", "some_class_name");
}

As well you could extend HTMLElement object, in order to add methods to add, remove, toggle and check classes (gist):

HTMLElement = typeof(HTMLElement) != 'undefiend' ? HTMLElement : Element;

HTMLElement.prototype.addClass = function(string) {
  if (!(string instanceof Array)) {
    string = string.split(' ');
  }
  for(var i = 0, len = string.length; i < len; ++i) {
    if (string[i] && !new RegExp('(\\s+|^)' + string[i] + '(\\s+|$)').test(this.className)) {
      this.className = this.className.trim() + ' ' + string[i];
    }
  }
}

HTMLElement.prototype.removeClass = function(string) {
  if (!(string instanceof Array)) {
    string = string.split(' ');
  }
  for(var i = 0, len = string.length; i < len; ++i) {
    this.className = this.className.replace(new RegExp('(\\s+|^)' + string[i] + '(\\s+|$)'), ' ').trim();
  }
}

HTMLElement.prototype.toggleClass = function(string) {
  if (string) {
    if (new RegExp('(\\s+|^)' + string + '(\\s+|$)').test(this.className)) {
      this.className = this.className.replace(new RegExp('(\\s+|^)' + string + '(\\s+|$)'), ' ').trim();
    } else {
      this.className = this.className.trim() + ' ' + string;
    }
  }
}

HTMLElement.prototype.hasClass = function(string) {
  return string && new RegExp('(\\s+|^)' + string + '(\\s+|$)').test(this.className);
}

And then just use like this (on click will add or remove class):

document.getElementById('yourElementId').onclick = function() {
  this.toggleClass('active');
}

Here is demo.


Just to add on information from another popular framework, Google Closures, see their dom/classes class:

goog.dom.classes.add(element, var_args)

goog.dom.classes.addRemove(element, classesToRemove, classesToAdd)

goog.dom.classes.remove(element, var_args)

One option for selecting the element is using goog.dom.query with a CSS3 selector:

var myElement = goog.dom.query("#MyElement")[0];

Change an element's CSS class with JavaScript in ASP.NET:

Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
    If Not Page.IsPostBack Then
        lbSave.Attributes.Add("onmouseover", "this.className = 'LinkButtonStyle1'")
        lbSave.Attributes.Add("onmouseout", "this.className = 'LinkButtonStyle'")
        lbCancel.Attributes.Add("onmouseover", "this.className = 'LinkButtonStyle1'")
        lbCancel.Attributes.Add("onmouseout", "this.className = 'LinkButtonStyle'")
    End If
End Sub

A couple of minor notes and tweaks on the previous regexes:

You'll want to do it globally in case the class list has the class name more than once. And, you'll probably want to strip spaces from the ends of the class list and convert multiple spaces to one space to keep from getting runs of spaces. None of these things should be a problem if the only code dinking with the class names uses the regex below and removes a name before adding it. But. Well, who knows who might be dinking with the class name list.

This regex is case insensitive so that bugs in class names may show up before the code is used on a browser that doesn't care about case in class names.

var s = "testing   one   four  one  two";
var cls = "one";
var rg          = new RegExp("(^|\\s+)" + cls + "(\\s+|$)", 'ig');
alert("[" + s.replace(rg, ' ') + "]");
var cls = "test";
var rg          = new RegExp("(^|\\s+)" + cls + "(\\s+|$)", 'ig');
alert("[" + s.replace(rg, ' ') + "]");
var cls = "testing";
var rg          = new RegExp("(^|\\s+)" + cls + "(\\s+|$)", 'ig');
alert("[" + s.replace(rg, ' ') + "]");
var cls = "tWo";
var rg          = new RegExp("(^|\\s+)" + cls + "(\\s+|$)", 'ig');
alert("[" + s.replace(rg, ' ') + "]");

I would use jQuery and write something like this:

jQuery(function($) {
    $("#some-element").click(function() {
        $(this).toggleClass("clicked");
    });
});

This code adds a function to be called when an element of the id some-element is clicked. The function appends clicked to the element's class attribute if it's not already part of it, and removes it if it's there.

Yes you do need to add a reference to the jQuery library in your page to use this code, but at least you can feel confident the most functions in the library would work on pretty much all the modern browsers, and it will save you time implementing your own code to do the same.

Thanks


The line

document.getElementById("MyElement").className = document.getElementById("MyElement").className.replace(/\bMyClass\b/','')

should be:

document.getElementById("MyElement").className = document.getElementById("MyElement").className.replace('/\bMyClass\b/','');

Here's my version, fully working:

function addHTMLClass(item, classname) {
    var obj = item
    if (typeof item=="string") {
        obj = document.getElementById(item)
    }
    obj.className += " " + classname
}

function removeHTMLClass(item, classname) {
    var obj = item
    if (typeof item=="string") {
        obj = document.getElementById(item)
    }
    var classes = ""+obj.className
    while (classes.indexOf(classname)>-1) {
        classes = classes.replace (classname, "")
    }
    obj.className = classes
}

Usage:

<tr onmouseover='addHTMLClass(this,"clsSelected")'
onmouseout='removeHTMLClass(this,"clsSelected")' >

Here's a toggleClass to toggle/add/remove a class on an element:

// If newState is provided add/remove theClass accordingly, otherwise toggle theClass
function toggleClass(elem, theClass, newState) {
    var matchRegExp = new RegExp('(?:^|\\s)' + theClass + '(?!\\S)', 'g');
    var add=(arguments.length>2 ? newState : (elem.className.match(matchRegExp) == null));

    elem.className=elem.className.replace(matchRegExp, ''); // clear all
    if (add) elem.className += ' ' + theClass;
}

see jsfiddle

also see my answer here for creating a new class dynamically


Change an element's class in vanilla JavaScript with IE6 support

You may try to use node attributes property to keep compatibility with old browsers even IE6:

function getClassNode(element) {
  for (var i = element.attributes.length; i--;)
    if (element.attributes[i].nodeName === 'class')
      return element.attributes[i];
}

function removeClass(classNode, className) {
  var index, classList = classNode.value.split(' ');
  if ((index = classList.indexOf(className)) > -1) {
    classList.splice(index, 1);
    classNode.value = classList.join(' ');
  }
}

function hasClass(classNode, className) {
  return classNode.value.indexOf(className) > -1;
}

function addClass(classNode, className) {
  if (!hasClass(classNode, className))
    classNode.value += ' ' + className;
}

document.getElementById('message').addEventListener('click', function() {
  var classNode = getClassNode(this);
  var className = hasClass(classNode, 'red') && 'blue' || 'red';

  removeClass(classNode, 'red');
  removeClass(classNode, 'blue');

  addClass(classNode, className);
})
.red {
  color: red;
}
.red:before {
  content: 'I am red! ';
}
.red:after {
  content: ' again';
}
.blue {
  color: blue;
}
.blue:before {
  content: 'I am blue! '
}
<span id="message" class="">Click me</span>


I use the following vanilla JavaScript functions in my code. They use regular expressions and indexOf but do not require quoting special characters in regular expressions.

function addClass(el, cn) {
    var c0 = (" " + el.className + " ").replace(/\s+/g, " "),
        c1 = (" " + cn + " ").replace(/\s+/g, " ");
    if (c0.indexOf(c1) < 0) {
        el.className = (c0 + c1).replace(/\s+/g, " ").replace(/^ | $/g, "");
    }
}

function delClass(el, cn) {
    var c0 = (" " + el.className + " ").replace(/\s+/g, " "),
        c1 = (" " + cn + " ").replace(/\s+/g, " ");
    if (c0.indexOf(c1) >= 0) {
        el.className = c0.replace(c1, " ").replace(/\s+/g, " ").replace(/^ | $/g, "");
    }
}

You can also use element.classList in modern browsers.


Just thought I'd throw this in:

function inArray(val, ary){
  for(var i=0,l=ary.length; i<l; i++){
    if(ary[i] === val){
      return true;
    }
  }
  return false;
}
function removeClassName(classNameS, fromElement){
  var x = classNameS.split(/\s/), s = fromElement.className.split(/\s/), r = [];
  for(var i=0,l=s.length; i<l; i++){
    if(!iA(s[i], x))r.push(s[i]);
  }
  fromElement.className = r.join(' ');
}
function addClassName(classNameS, toElement){
  var s = toElement.className.split(/\s/);
  s.push(c); toElement.className = s.join(' ');
}

just say myElement.classList="new-class" unless you need to maintain other existing classes in which case you can use the classList.add, .remove methods.

var doc = document;
var divOne = doc.getElementById("one");
var goButton = doc.getElementById("go");

goButton.addEventListener("click", function() {
  divOne.classList="blue";
});
div{
  min-height:48px;
  min-width:48px;
}
.bordered{
  border: 1px solid black;
}
.green{
  background:green;
}
.blue{
  background: blue;
}
<button id="go">Change Class</button>

<div id="one" class="bordered green">

</div>


OK, I think in this case you should use jQuery or write your own Methods in pure javascript, my preference is adding my own methods rather than injecting all jQuery to my application if I don't need that for other reasons.

I'd like to do something like below as methods to my javascript framework to add few functionalities which handle adding classes, deleting classes, etc similar to jQuery, this is fully supported in IE9+, also my code is written in ES6, so you need to make sure your browser support it or you using something like babel, otherwise need to use ES5 syntax in your code, also in this way, we finding element via ID, which means the element needs to have an ID to be selected:

//simple javascript utils for class management in ES6
var classUtil = {

  addClass: (id, cl) => {
    document.getElementById(id).classList.add(cl);
  },

  removeClass: (id, cl) => {
    document.getElementById(id).classList.remove(cl);
  },

  hasClass: (id, cl) => {
    return document.getElementById(id).classList.contains(cl);
  },

  toggleClass: (id, cl) => {
    document.getElementById(id).classList.toggle(cl);
  }

}

and you can simply call use them as below, imagine your element has id of 'id' and class of 'class', make sure you pass them as a string, you can use the util as below:

classUtil.addClass('myId', 'myClass');
classUtil.removeClass('myId', 'myClass');
classUtil.hasClass('myId', 'myClass');
classUtil.toggleClass('myId', 'myClass');

classList DOM API:

A very convenient manner of adding and removing classes is the classList DOM API. This API allows us to select all classes of a specific DOM element in order to modify the list using javascript. For example:

const el = document.getElementById("main");
console.log(el.classList);
<div class="content wrapper animated" id="main"></div>

We can observe in the log that we are getting back an object with not only the classes of the element, but also many auxiliary methods and properties. This object inherits from the interface DOMTokenList, an interface which is used in the DOM to represent a set of space separated tokens (like classes).

Example:

const el = document.getElementById('container');


function addClass () {
   el.classList.add('newclass');
}


function replaceClass () {
     el.classList.replace('foo', 'newFoo');
}


function removeClass () {
       el.classList.remove('bar');
}
button{
  margin: 20px;
}

.foo{
  color: red;
}

.newFoo {
  color: blue;
}

.bar{
  background-color:powderblue;
}

.newclass{
  border: 2px solid green;
}
<div class="foo bar" id="container">
  "Sed ut perspiciatis unde omnis 
  iste natus error sit voluptatem accusantium doloremque laudantium, 
  totam rem aperiam, eaque ipsa quae ab illo inventore veritatis et 
  quasi architecto beatae vitae dicta sunt explicabo. Nemo enim ipsam 
  voluptatem quia voluptas 
 </div>
  
<button onclick="addClass()">AddClass</button>
  
<button onclick="replaceClass()">ReplaceClass</button>
  
<button onclick="removeClass()">removeClass</button>
  


Yes there is many ways to do this. In ES6 syntax we can achieve easily. Use this code toggle add and remove class.

const tabs=document.querySelectorAll('.menu li');

for(let tab of tabs){
  
  tab.onclick=function(){
    
  let activetab=document.querySelectorAll('li.active');
    
  activetab[0].classList.remove('active')
  
    tab.classList.add('active'); 
  }
  
}
body {
    padding:20px;
    font-family:sans-serif;    
}

ul {
    margin:20px 0;
    list-style:none;
}

li {
    background:#dfdfdf;
    padding:10px;
    margin:6px 0;
    cursor:pointer;
}

li.active {
    background:#2794c7;
    font-weight:bold;
    color:#ffffff;
}
<i>Please click an item:</i>

<ul class="menu">
  <li class="active"><span>Three</span></li>
  <li><span>Two</span></li>
  <li><span>One</span></li>
</ul>


try

function change(el) { el.className='second' }
.first { width: 50px; height: 50px; background: blue }
.second { width: 150px; height: 150px; background: red; transition: all 0.3s ease-in }
<button  onclick="change(box)">Click me</button>
<div id="box" class="first"></div>


function classed(el, class_name, add_class) {
  const re = new RegExp("(?:^|\\s)" + class_name + "(?!\\S)", "g");
  if (add_class && !el.className.match(re)) el.className += " " + class_name
  else if (!add_class) el.className = el.className.replace(re, '');
}

using the accepted answer above here is a simple cross-browser function to add and remove class

add class:

classed(document.getElementById("denis"), "active", true)

remove class:

classed(document.getElementById("denis"), "active", false)

Lots of answers, lots of good answers.

TL;DR :

document.getElementById('id').className = 'class'

OR

document.getElementById('id').classList.add('class');
document.getElementById('id').classList.remove('class');

That's it.

And, if you really want to know the why and educate yourself then I suggest reading Peter Boughton's answer, it's perfect.

Note:
This is possible with (document or event):

  • getElementById()
  • getElementsByClassName()
  • querySelector()
  • querySelectorAll()

Working JavaScript code:

<div id="div_add" class="div_add">Add class from Javascript</div>
<div id="div_replace" class="div_replace">Replace class from Javascript</div>
<div id="div_remove" class="div_remove">Remove class from Javascript</div>
<button onClick="div_add_class();">Add class from Javascript</button>
<button onClick="div_replace_class();">Replace class from Javascript</button>
<button onClick="div_remove_class();">Remove class from Javascript</button>
<script type="text/javascript">
    function div_add_class()
    {
        document.getElementById("div_add").className += " div_added";
    }
    function div_replace_class()
    {
        document.getElementById("div_replace").className = "div_replaced";
    }
    function div_remove_class()
    {
        document.getElementById("div_remove").className = "";
    }
</script>

You can download a working code from this link.


Here is simple jQuery code to do that.

$(".class1").click(function(argument) {
    $(".parentclass").removeClass("classtoremove");
    setTimeout(function (argument) {
        $(".parentclass").addClass("classtoadd");
    }, 100);
});

Here,

  • Class1 is a listener for an event.
  • The parent class is the class which hosts the class you want to change
  • Classtoremove is the old class you have.
  • Class to add is the new class that you want to add.
  • 100 is the timeout delay during which the class is changed.

Good Luck.


This is easiest with a library like jQuery:

<input type="button" onClick="javascript:test_byid();" value="id='second'" />

<script>
function test_byid()
{
    $("#second").toggleClass("highlight");
}
</script>

No offense, but it's unclever to change class on-the-fly as it forces the CSS interpreter to recalculate the visual presentation of the entire web page.

The reason is that it is nearly impossible for the CSS interpreter to know if any inheritance or cascading could be changed, so the short answer is:

Never ever change className on-the-fly !-)

But usually you'll only need to change a property or two, and that is easily implemented:

function highlight(elm){
    elm.style.backgroundColor ="#345";
    elm.style.color = "#fff";
}

There is a property className in javascript to change the name of the class of an HTML element. The existing class value will be replaced with the new one, that you have assigned in className.

<!DOCTYPE html>
<html>
<head>
<title>How to change class of an HTML element in Javascript?</title>
<link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/font-awesome/4.7.0/css/font-awesome.min.css">
</head>
<body>
<h1 align="center"><i class="fa fa-home" id="icon"></i></h1><br />

<center><button id="change-class">Change Class</button></center>

<script>
var change_class=document.getElementById("change-class");
change_class.onclick=function()
{
    var icon=document.getElementById("icon");
    icon.className="fa fa-gear";
}

</script>
</body>
</html>

Credit - https://jaischool.com/javascript-lang/how-to-change-class-name-of-an-html-element-in-javascript.html


The OP question was How can I change an element's class with JavaScript?

Modern browsers allow you to do this with one line of javascript:

document.getElementById('id').classList.replace('span1','span2')

The classList attribute provides a DOMTokenList which has a variety of methods. You can operate on an element's classList using simple manipulations like add(), remove() or replace(). Or get very sophisticated and manipulate classes like you would an object or Map with keys(), values(), entries()