Javascript format function to replace placeholders in a string with content

gistfile1.js

// usage:
// string.format({key: replacement})
//
// example:
// 'Hello {name}, how are you doing? I am doing {mood}.'.format({name: 'Mike', mood: 'fine'});
String.prototype.format = function() {
    var formatted = this;
    if (arguments.length && typeof arguments[0] == 'object') {
        var vars = arguments[0];
        for (v in vars) {
            var regexp = new RegExp('\\{'+v+'\\}', 'gi');
            formatted = formatted.replace(regexp, vars[v]);
        }
    }
    return formatted;
};