guid.js

var guid = (function(){
    function hasUniqueNumber(){
        var docEl = document.documentElement, elem = document.createElement("div");
        return (typeof elem.uniqueNumber == "number" && typeof docEl.uniqueNumber == "number" &&
            elem.uniqueNumber != docEl.uniqueNumber);
    }

    var guid, last = 1;

    if(hasUniqueNumber()){
        guid = function guid(obj){
            if(obj){
                if(typeof obj.uniqueNumber == "number"){
                    return obj.uniqueNumber;
                }else if(typeof obj.guid == "number"){
                    return obj.guid;
                }

                return obj.guid = last++;
            }
        };
    }else{
        guid = function guid(obj){
            if(obj){
                if(typeof obj.guid == "number"){
                    return obj.guid;
                }

                return obj.guid = last++;
            }
        };
    }
    return guid;
})();