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

How can I change the class of an HTML element in response to an onclick or any other events using JavaScript?

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");
}

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>

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()

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, ' ') + "]");

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()

Peter Boughton's answer is a great one but it's now over a decade old. All modern browsers now support DOMTokenList - see https://caniuse.com/#search=classList and even IE11 supports some DOMTokenList methods

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.

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) {_x000D_
  for (var i = element.attributes.length; i--;)_x000D_
    if (element.attributes[i].nodeName === 'class')_x000D_
      return element.attributes[i];_x000D_
}_x000D_
_x000D_
function removeClass(classNode, className) {_x000D_
  var index, classList = classNode.value.split(' ');_x000D_
  if ((index = classList.indexOf(className)) > -1) {_x000D_
    classList.splice(index, 1);_x000D_
    classNode.value = classList.join(' ');_x000D_
  }_x000D_
}_x000D_
_x000D_
function hasClass(classNode, className) {_x000D_
  return classNode.value.indexOf(className) > -1;_x000D_
}_x000D_
_x000D_
function addClass(classNode, className) {_x000D_
  if (!hasClass(classNode, className))_x000D_
    classNode.value += ' ' + className;_x000D_
}_x000D_
_x000D_
document.getElementById('message').addEventListener('click', function() {_x000D_
  var classNode = getClassNode(this);_x000D_
  var className = hasClass(classNode, 'red') && 'blue' || 'red';_x000D_
_x000D_
  removeClass(classNode, 'red');_x000D_
  removeClass(classNode, 'blue');_x000D_
_x000D_
  addClass(classNode, className);_x000D_
})

.red {_x000D_
  color: red;_x000D_
}_x000D_
.red:before {_x000D_
  content: 'I am red! ';_x000D_
}_x000D_
.red:after {_x000D_
  content: ' again';_x000D_
}_x000D_
.blue {_x000D_
  color: blue;_x000D_
}_x000D_
.blue:before {_x000D_
  content: 'I am blue! '_x000D_
}

<span id="message" class="">Click me</span>

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/','');

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>

try

element.className='second'

function change(box) { box.className='second' }

.first  { width:  70px; height:  70px; background: #ff0                 }_x000D_
.second { width: 150px; height: 150px; background: #f00; transition: 1s }

<div onclick="change(this)" class="first">Click me</div>

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'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

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

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, ' ') + "]");

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/','');

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(' ');
}

You can use node.className like so:

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

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

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 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;_x000D_
var divOne = doc.getElementById("one");_x000D_
var goButton = doc.getElementById("go");_x000D_
_x000D_
goButton.addEventListener("click", function() {_x000D_
  divOne.classList="blue";_x000D_
});

div{_x000D_
  min-height:48px;_x000D_
  min-width:48px;_x000D_
}_x000D_
.bordered{_x000D_
  border: 1px solid black;_x000D_
}_x000D_
.green{_x000D_
  background:green;_x000D_
}_x000D_
.blue{_x000D_
  background: blue;_x000D_
}

<button id="go">Change Class</button>_x000D_
_x000D_
<div id="one" class="bordered green">_x000D_
_x000D_
</div>

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.

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";
}

You can use node.className like so:

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

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

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);
    }
}

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];

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()

Peter Boughton's answer is a great one but it's now over a decade old. All modern browsers now support DOMTokenList - see https://caniuse.com/#search=classList and even IE11 supports some DOMTokenList methods

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');_x000D_
_x000D_
for(let tab of tabs){_x000D_
  _x000D_
  tab.onclick=function(){_x000D_
    _x000D_
  let activetab=document.querySelectorAll('li.active');_x000D_
    _x000D_
  activetab[0].classList.remove('active')_x000D_
  _x000D_
    tab.classList.add('active'); _x000D_
  }_x000D_
  _x000D_
}

body {_x000D_
    padding:20px;_x000D_
    font-family:sans-serif;    _x000D_
}_x000D_
_x000D_
ul {_x000D_
    margin:20px 0;_x000D_
    list-style:none;_x000D_
}_x000D_
_x000D_
li {_x000D_
    background:#dfdfdf;_x000D_
    padding:10px;_x000D_
    margin:6px 0;_x000D_
    cursor:pointer;_x000D_
}_x000D_
_x000D_
li.active {_x000D_
    background:#2794c7;_x000D_
    font-weight:bold;_x000D_
    color:#ffffff;_x000D_
}

<i>Please click an item:</i>_x000D_
_x000D_
<ul class="menu">_x000D_
  <li class="active"><span>Three</span></li>_x000D_
  <li><span>Two</span></li>_x000D_
  <li><span>One</span></li>_x000D_
</ul>

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");_x000D_
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');_x000D_
_x000D_
_x000D_
function addClass () {_x000D_
   el.classList.add('newclass');_x000D_
}_x000D_
_x000D_
_x000D_
function replaceClass () {_x000D_
     el.classList.replace('foo', 'newFoo');_x000D_
}_x000D_
_x000D_
_x000D_
function removeClass () {_x000D_
       el.classList.remove('bar');_x000D_
}

button{_x000D_
  margin: 20px;_x000D_
}_x000D_
_x000D_
.foo{_x000D_
  color: red;_x000D_
}_x000D_
_x000D_
.newFoo {_x000D_
  color: blue;_x000D_
}_x000D_
_x000D_
.bar{_x000D_
  background-color:powderblue;_x000D_
}_x000D_
_x000D_
.newclass{_x000D_
  border: 2px solid green;_x000D_
}

<div class="foo bar" id="container">_x000D_
  "Sed ut perspiciatis unde omnis _x000D_
  iste natus error sit voluptatem accusantium doloremque laudantium, _x000D_
  totam rem aperiam, eaque ipsa quae ab illo inventore veritatis et _x000D_
  quasi architecto beatae vitae dicta sunt explicabo. Nemo enim ipsam _x000D_
  voluptatem quia voluptas _x000D_
 </div>_x000D_
  _x000D_
<button onclick="addClass()">AddClass</button>_x000D_
  _x000D_
<button onclick="replaceClass()">ReplaceClass</button>_x000D_
  _x000D_
<button onclick="removeClass()">removeClass</button>_x000D_
  

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

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";
}

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")' >

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()

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.

You can use node.className like so:

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

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

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

You can use node.className like so:

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

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

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);
    }
}

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")

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>

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.

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")

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

try

element.className='second'

function change(box) { box.className='second' }

.first  { width:  70px; height:  70px; background: #ff0                 }_x000D_
.second { width: 150px; height: 150px; background: #f00; transition: 1s }

<div onclick="change(this)" class="first">Click me</div>

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.

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")' >

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

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

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.

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";
}

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

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");
}

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');_x000D_
_x000D_
for(let tab of tabs){_x000D_
  _x000D_
  tab.onclick=function(){_x000D_
    _x000D_
  let activetab=document.querySelectorAll('li.active');_x000D_
    _x000D_
  activetab[0].classList.remove('active')_x000D_
  _x000D_
    tab.classList.add('active'); _x000D_
  }_x000D_
  _x000D_
}

body {_x000D_
    padding:20px;_x000D_
    font-family:sans-serif;    _x000D_
}_x000D_
_x000D_
ul {_x000D_
    margin:20px 0;_x000D_
    list-style:none;_x000D_
}_x000D_
_x000D_
li {_x000D_
    background:#dfdfdf;_x000D_
    padding:10px;_x000D_
    margin:6px 0;_x000D_
    cursor:pointer;_x000D_
}_x000D_
_x000D_
li.active {_x000D_
    background:#2794c7;_x000D_
    font-weight:bold;_x000D_
    color:#ffffff;_x000D_
}

<i>Please click an item:</i>_x000D_
_x000D_
<ul class="menu">_x000D_
  <li class="active"><span>Three</span></li>_x000D_
  <li><span>Two</span></li>_x000D_
  <li><span>One</span></li>_x000D_
</ul>

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.

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");_x000D_
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');_x000D_
_x000D_
_x000D_
function addClass () {_x000D_
   el.classList.add('newclass');_x000D_
}_x000D_
_x000D_
_x000D_
function replaceClass () {_x000D_
     el.classList.replace('foo', 'newFoo');_x000D_
}_x000D_
_x000D_
_x000D_
function removeClass () {_x000D_
       el.classList.remove('bar');_x000D_
}

button{_x000D_
  margin: 20px;_x000D_
}_x000D_
_x000D_
.foo{_x000D_
  color: red;_x000D_
}_x000D_
_x000D_
.newFoo {_x000D_
  color: blue;_x000D_
}_x000D_
_x000D_
.bar{_x000D_
  background-color:powderblue;_x000D_
}_x000D_
_x000D_
.newclass{_x000D_
  border: 2px solid green;_x000D_
}

<div class="foo bar" id="container">_x000D_
  "Sed ut perspiciatis unde omnis _x000D_
  iste natus error sit voluptatem accusantium doloremque laudantium, _x000D_
  totam rem aperiam, eaque ipsa quae ab illo inventore veritatis et _x000D_
  quasi architecto beatae vitae dicta sunt explicabo. Nemo enim ipsam _x000D_
  voluptatem quia voluptas _x000D_
 </div>_x000D_
  _x000D_
<button onclick="addClass()">AddClass</button>_x000D_
  _x000D_
<button onclick="replaceClass()">ReplaceClass</button>_x000D_
  _x000D_
<button onclick="removeClass()">removeClass</button>_x000D_
  

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');

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');

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];

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');

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');

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;_x000D_
var divOne = doc.getElementById("one");_x000D_
var goButton = doc.getElementById("go");_x000D_
_x000D_
goButton.addEventListener("click", function() {_x000D_
  divOne.classList="blue";_x000D_
});

div{_x000D_
  min-height:48px;_x000D_
  min-width:48px;_x000D_
}_x000D_
.bordered{_x000D_
  border: 1px solid black;_x000D_
}_x000D_
.green{_x000D_
  background:green;_x000D_
}_x000D_
.blue{_x000D_
  background: blue;_x000D_
}

<button id="go">Change Class</button>_x000D_
_x000D_
<div id="one" class="bordered green">_x000D_
_x000D_
</div>

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

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) {_x000D_
  for (var i = element.attributes.length; i--;)_x000D_
    if (element.attributes[i].nodeName === 'class')_x000D_
      return element.attributes[i];_x000D_
}_x000D_
_x000D_
function removeClass(classNode, className) {_x000D_
  var index, classList = classNode.value.split(' ');_x000D_
  if ((index = classList.indexOf(className)) > -1) {_x000D_
    classList.splice(index, 1);_x000D_
    classNode.value = classList.join(' ');_x000D_
  }_x000D_
}_x000D_
_x000D_
function hasClass(classNode, className) {_x000D_
  return classNode.value.indexOf(className) > -1;_x000D_
}_x000D_
_x000D_
function addClass(classNode, className) {_x000D_
  if (!hasClass(classNode, className))_x000D_
    classNode.value += ' ' + className;_x000D_
}_x000D_
_x000D_
document.getElementById('message').addEventListener('click', function() {_x000D_
  var classNode = getClassNode(this);_x000D_
  var className = hasClass(classNode, 'red') && 'blue' || 'red';_x000D_
_x000D_
  removeClass(classNode, 'red');_x000D_
  removeClass(classNode, 'blue');_x000D_
_x000D_
  addClass(classNode, className);_x000D_
})

.red {_x000D_
  color: red;_x000D_
}_x000D_
.red:before {_x000D_
  content: 'I am red! ';_x000D_
}_x000D_
.red:after {_x000D_
  content: ' again';_x000D_
}_x000D_
.blue {_x000D_
  color: blue;_x000D_
}_x000D_
.blue:before {_x000D_
  content: 'I am blue! '_x000D_
}

<span id="message" class="">Click me</span>

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

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(' ');
}

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.

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)

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>