if (!Array.prototype.push) Array.prototype.push = function() {

    for (var i=0; i<arguments.length; i++) this[this.length] = arguments[i];

    return this.length;

}



Array.prototype.find = function(value, start) {

    start = start || 0;

    for (var i=start; i<this.length; i++)

        if (this[i]==value)

            return i;

    return -1;

}



Array.prototype.has = function(value) {

    return this.find(value)!==-1;

}



// FUNCTIONAL



function map(list, func) {

    var result = [];

    func = func || function(v) {return v};

    for (var i=0; i < list.length; i++) result.push(func(list[i], i, list));

    return result;

}



function filter(list, func) {

    var result = [];

    func = func || function(v) {return v};

    map(list, function(v) { if (func(v)) result.push(v) } );

    return result;

}





// DOM



function getElem(elem) {

    if (document.getElementById) {

        if (typeof elem == "string") {

            elem = document.getElementById(elem);

            if (elem===null) throw 'cannot get element: element does not exist';

        } else if (typeof elem != "object") {

            throw 'cannot get element: invalid datatype';

        }

    } else throw 'cannot get element: unsupported DOM';

    return elem;

}



function hasClass(elem, className) {

    return getElem(elem).className.split(' ').has(className);

}



function getElementsByClass(className, tagName, parentNode) {

    parentNode = !isUndefined(parentNode)? getElem(parentNode) : document;

    if (isUndefined(tagName)) tagName = '*';

    return filter(parentNode.getElementsByTagName(tagName),

        function(elem) { return hasClass(elem, className) });

}





// DOM EVENTS



function listen(event, elem, func) {

    elem = getElem(elem);

    if (elem.addEventListener)  // W3C DOM

        elem.addEventListener(event,func,false);

    else if (elem.attachEvent)  // IE DOM

        elem.attachEvent('on'+event, function(){ func(new W3CDOM_Event(elem)) } );

        // for IE we use a wrapper function that passes in a simplified faux Event object.

    else throw 'cannot add event listener';

}



function mlisten(event, elem_list, func) {

    map(elem_list, function(elem) { listen(event, elem, func) } );

}



function W3CDOM_Event(currentTarget) {

    this.currentTarget  = currentTarget;

    this.preventDefault = function() { window.event.returnValue = false }

    return this;

}





// MISC CLEANING-AFTER-MICROSOFT STUFF



function isUndefined(v) {

    var undef;

    return v===undef;

}