[javascript] Remove CSS class from element with JavaScript (no jQuery)

Could anyone let me know how to remove a class on an element using JavaScript only? Please do not give me an answer with jQuery as I can't use it, and I don't know anything about it.

document.getElementById("whatever").className += "classToKeep";

With the plus sign ('+') appending the class as opposed to overwriting any existing classes

try:

function removeClassName(elem, name){
    var remClass = elem.className;
    var re = new RegExp('(^| )' + name + '( |$)');
    remClass = remClass.replace(re, '$1');
    remClass = remClass.replace(/ $/, '');
    elem.className = remClass;
}

Here's a way to bake this functionality right into all DOM elements:

HTMLElement.prototype.removeClass = function(remove) {
    var newClassName = "";
    var i;
    var classes = this.className.split(" ");
    for(i = 0; i < classes.length; i++) {
        if(classes[i] !== remove) {
            newClassName += classes[i] + " ";
        }
    }
    this.className = newClassName;
}

The right and standard way to do it is using classList. It is now widely supported in the latest version of most modern browsers:

ELEMENT.classList.remove("CLASS_NAME");

remove.onclick = () => {_x000D_
  const el = document.querySelector('#el');_x000D_
  if (el.classList.contains("red")) {_x000D_
    el.classList.remove("red");_x000D_
_x000D_
  }_x000D_
}

.red {_x000D_
  background: red_x000D_
}

<div id='el' class="red"> Test</div>_x000D_
<button id='remove'>Remove Class</button>

Documentation: https://developer.mozilla.org/en/DOM/element.classList

Edit

Okay, complete re-write. It's been a while, I've learned a bit and the comments have helped.

Node.prototype.hasClass = function (className) {
    if (this.classList) {
        return this.classList.contains(className);
    } else {
        return (-1 < this.className.indexOf(className));
    }
};

Node.prototype.addClass = function (className) {
    if (this.classList) {
        this.classList.add(className);
    } else if (!this.hasClass(className)) {
        var classes = this.className.split(" ");
        classes.push(className);
        this.className = classes.join(" ");
    }
    return this;
};

Node.prototype.removeClass = function (className) {
    if (this.classList) {
        this.classList.remove(className);
    } else {
        var classes = this.className.split(" ");
        classes.splice(classes.indexOf(className), 1);
        this.className = classes.join(" ");
    }
    return this;
};

// Some browsers don't have a native trim() function
if(!String.prototype.trim) {
    Object.defineProperty(String.prototype,'trim', {
        value: function() {
            return this.replace(/^\s+|\s+$/g,'');
        },
        writable:false,
        enumerable:false,
        configurable:false
    });
}
// addClass()
// first checks if the class name already exists, if not, it adds the class.
Object.defineProperty(Node.prototype,'addClass', {
    value: function(c) {
        if(this.className.indexOf(c)<0) {
            this.className=this.className+=' '+c;
        }
        return this;
    },
    writable:false,
    enumerable:false,
    configurable:false
});
// removeClass()
// removes the class and cleans up the className value by changing double 
// spacing to single spacing and trimming any leading or trailing spaces
Object.defineProperty(Node.prototype,'removeClass', {
    value: function(c) {
        this.className=this.className.replace(c,'').replace('  ',' ').trim();
        return this;
    },
    writable:false,
    enumerable:false,
    configurable:false
});

Now you can call myElement.removeClass('myClass')

or chain it: myElement.removeClass("oldClass").addClass("newClass");

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

where MyID is the ID of the element and MyClass is the name of the class you wish to remove.

UPDATE: To support class names containing dash character, such as "My-Class", use

document.getElementById("MyID").className =
  document.getElementById("MyID").className
    .replace(new RegExp('(?:^|\\s)'+ 'My-Class' + '(?:\\s|$)'), ' ');

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

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

I use this JS snippet code :

First of all, I reach all the classes then according to index of my target class, I set className = "".

Target = document.getElementsByClassName("yourClass")[1];
Target.className="";

var element = document.getElementById('example_id');
var remove_class = 'example_class';

element.className = element.className.replace(' ' + remove_class, '').replace(remove_class, '');

It's very simple, I think.

document.getElementById("whatever").classList.remove("className");

div.classList.add("foo");
div.classList.remove("foo");

More at https://developer.mozilla.org/en-US/docs/Web/API/element.classList