format string "Hello {0}, {1}"

format.js

/** format string
* format("Hello {0}! {1}-{2}.", "World", "foo", "bar") --> "Hello World! foo-bar."
*/
function format(string, etc) {
	var args = arguments;
	return string.replace(/{(\d+)}/g, function(match, number) {
		return typeof args[+number+1]!="undefined" ? args[+number+1] : match;
	});
}

/** format string
* "Hello {0}! {1}-{2}.".format("World","foo","bar") --> "Hello World! foo-bar."
*/
String.prototype.format = function() {
	var args = arguments;
	return this.replace(/{(\d+)}/g, function(bracket, n) { 
		return typeof args[+n]!="undefined"? args[+n] : bracket;
	});
};