Implement a format function similar to Python's in JavaScript

python-string-format.js

// Check if it's not implemented first. Source: https://stackoverflow.com/a/4673436
if (!String.prototype.format) {
    String.prototype.format = function() {
        var args = arguments;
        return this.replace(/{(\d+)}/g, function(match, number) { 
            return typeof args[number] != 'undefined'
                ? args[number]
                : match
            ;
        });
    };
}