.Net's String.Format is a very powerful method for working with strings and is one of my favorite utility which I have been using in C# & VB.net since long. And while working with javascript, lot many times I thought if we had something equivelent to .Net's  String.Format in javascript. Finally after goggling and taking help form few blogs I finally wrote following String.Format function into my javascript library.

String.format = function (text) {


    //check if there are two arguments in the arguments list

    if (arguments.length <= 1) {

        //if there are not 2 or more arguments there's nothing to replace

        //just return the original text

        return text;

    }


    //decrement to move to the second argument in the array

    var tokenCount = arguments.length - 2;

    for (var token = 0; token <= tokenCount; token++) {

        //iterate through the tokens and replace their

        // placeholders from the original text in order

        text = text.replace(new RegExp("{" + token + "}", "gi"),

                                                arguments[token + 1]);

    }

    return text;

};
The above code creates static function String.format and below is the working example of it: 
var result = String.format("Sum of {0} and {1} is {2).", 5,6,5+6)


//This results in

result = "Sum of 5 and 6 is 11."
This functionality can also be written in inline flavor: 
String.prototype.format = function () {

	var txt = this;

	for(var i=0;i<arguments.length;i++)

	{

		var exp = new RegExp('{' + (i) + '}','gm');

		txt = txt.replace(exp,arguments[i]);

	}

	return txt;

}



Usage: 
var result = "Sum of {0} and {1} is {2).".format(5,6,5+6);

//This results in

result = "Sum of 5 and 6 is 11."
Related Links:

Trim() functionality in JavaScript