function StringFormatter(){
}
StringFormatter.prototype.format = function(str) {
    var i = 1;
    while(i < arguments.length){
        var delimiter = "[" + (i-1) + "]";
        var pos = str.indexOf(delimiter);
        if(pos > -1){
            var s = str.substring(0, pos) + arguments[i];
            str = s + str.substring(pos + delimiter.length, str.length);
        }
        i++;
    }
    return str;
}

var MessageFormat = new StringFormatter();