class manipulation.

gistfile1.js

Element.prototype.addClass = function(c) {
    if (!this.hasClass(c)) {
        this.className += " " + c;
    }
    return this;
};
NodeList.prototype.addClass = function(c) {
    for (var i = 0, l = this.length; i < l; i++) {
        this[i].addClass(c);
    }  
    return this;
};
Element.prototype.removeClass = function(c) {
    this.replaceClass(c, "");
    return this;
};
NodeList.prototype.removeClass = function(c) {
    for (var i = 0, l = this.length; i < l; i++) {
        this[i].removeClass(c);
    }  
    return this;
};
Element.prototype.replaceClass = function(oC, nC) {
    this.className = this.className.replace(new RegExp("(\\b|^)" + oC + "(\\b|$)"), nC);
    return this;
};
NodeList.prototype.replaceClass = function(oC, nC) {
    for (var i = 0, l = this.length; i < l; i++) {
        this[i].replaceClass(oC, nC);
    }
    return this;
};