stringFormat.js

function stringFormat(format, args) {
        if (arguments.length === 0) {
            throw "Missing arguments";
        }

        if (!args) {
            return format;
        }

        return format.replace(/{(\d+)}/g, function(match, number) {
            return typeof args[number] !== 'undefined' ? args[number] : match;
        });
    }

stringFormat("{0} {1} {2}", ["1", "22"])
// "1 22 {2}"
stringFormat("asd")
// "asd"