JS中String类型添加占位符功能

//String类型添加占位符功能
String.prototype.format = function(args){
    if (arguments.length > 0){
        var result = this;
        if (arguments.length == 1 && typeof (args) == "object"){
            for (var key in args){
                var reg = new RegExp("({" + key + "})", "g");
                result = result.replace(reg, args[key]);
            }
        }else{
            for (var i = 0; i < arguments.length; i++){
                if (arguments[i] == undefined){
                    return "";
                }
                else{
                    var reg = new RegExp("({[" + i + "]})", "g");
                    result = result.replace(reg, arguments[i]);
                }
            }
        }
        return result;
    }
    else{
        return this;
    }
}