JavaScript equivalent to C#'s string.Format(...) function

String.format.js

if (!String.prototype.format) {
    // Equivalent to C# String.Format
    String.prototype.format = function () {
        var args = arguments;
        return this.replace(/{(\d+)}/g, function (match, number) {
            return typeof args[number] != 'undefined'
                ? args[number]
                : match
                ;
        });
    };
}