gistfile1.txt

var format = function(str) {
	var args = Array.prototype.slice.call(arguments, 1);
	var replaceFunc = function(matchedStr) {
		var index = parseInt(matchedStr.substring(1, matchedStr.length-1), 10);
		return args[index] != null ? args[index] : '';
	};
	return str.replace(/\{[0-9]+\}/g, replaceFunc);				
};

format("Hello {0}", "world");