

Object.prototype.hasClass = function(className) {
   var pattern = new RegExp('(^|\\s)' + className + '(\\s|$)'); //use this regexp
   return pattern.test(this.className); //to check for the class
}
 
Object.prototype.addClass = function(className) {
   if (!this.hasClass(className)) { //if the class isn't there already
      this.className += (' ' + className); //append it to the end of the class list
   }
}
 
Object.prototype.removeClass = function(className) {
   var pattern = new RegExp('(^|\\s)' + className + '(\\s|$)'); //use this regexp
   this.className = this.className.replace(pattern, ' '); //to make a search and replace by a blank space

basic example:



.smalltext {
   font-size: 8px;
}

.bigtext {
   font-size: 15px;
}

colorblue {
   color: blue;
}

colorred {
   color: red;
}



This is some text



var el = document.getElementById('someelement');

if (el.hasClass('colorred'))
    el.removeClass('colorred');

el.addClass('colorblue');

//now the text in someelement is blue, but still has a size of 8px

el.removeClass('smalltext');

//now the text has the default size

el.addClass('bigtext');

//now it has 15 px