Summary of Javascript extending String methods_javascript skills

String.prototype.EndWith = function (str) {
    if (str == null || str == "" || this.length == 0 || str.length > this.length)
        return false;
    if (this.substring(this.length - str.length) == str)
        return true;
    else
        return false;
    return true;
}
String.prototype.StartWith = function (str) {
    if (str == null || str == "" || this.length == 0 || str.length > this.length)
        return false;
    if (this.substr(0, str.length) == str)
        return true;
    else
        return false;
    return true;
}
String.prototype.Trim = function () {
    return this.replace(/(^s*)|(s*$)/g, "");
}
String.prototype.ltrim = function () {
    return this.replace(/(^s*)/g, "");
}
String.prototype.rtrim = function () {
    return this.replace(/(s*$)/g, "");
}
String.format = function (str) {
    var i = 1, args = arguments;
    var str = args[0];
    var re = /{(d )}/g;
    return str.replace(re, function () { return args[i ] });
};
var Json2string = function (obj) {
            var t = typeof (obj);
            if (t != "object" || obj === null) {
                // simple data type        
                if (t == "string") obj = "'" obj "'";
                return String(obj);
            }
            else {
                // recurse array or object        
                var n, v, json = [], arr = (obj && obj.constructor == Array);
                for (n in obj) {
                    v = obj[n]; t = typeof (v);
                    if (t == "string") v = "'" v "'";
                    else if (t == "object" && v !== null)
                        v = Json2string(v);
                    json.push((arr ? "" : "'" n "':") String(v));
                }
                return (arr ? "[" : "{") String(json) (arr ? "]" : "}");
            }
        };