stringFormat.js

function stringFormat (formatString)
{
    var builder = [];

    var st = 0;
    var j = 0;

    for (var i = 0; i < formatString.length; i++)
    {
        switch (st)
        {
            case 0:
            {
                switch (formatString[i])
                {
                    case "{":

                        st = 1;
                        builder.push(formatString.substr(j, i - j));
                        j = i + 1;
                        break;

                    case "}":

                        st = 2;
                        builder.push(formatString.substr(j, i - j));
                        j = i + 1;
                        break;

                    default:

                        st = 0;
                        break;
                }
                break;
            }

            case 1:
            {
                switch (formatString[i])
                {
                    case "{":

                        builder.push("{");
                        j = i + 1;
                        st = 0;
                        break;

                    case "0":
                    case "1":
                    case "2":
                    case "3":
                    case "4":
                    case "5":
                    case "6":
                    case "7":
                    case "8":
                    case "9":

                        st = 3;
                        break;

                    default:

                        console.error("stringFormat: Pattern error processing string", formatString, "at index", i);
                        return null;
                }
                break;
            }

            case 2:
            {
                switch (formatString[i])
                {
                    case "}":

                        builder.push("}");
                        j = i + 1;
                        st = 0;
                        break;

                    default:

                        console.error("stringFormat: Pattern error processing string", formatString, "at index", i);
                        return null;
                }
                break;
            }

            case 3:
            {
                switch (formatString[i])
                {
                    case "0":
                    case "1":
                    case "2":
                    case "3":
                    case "4":
                    case "5":
                    case "6":
                    case "7":
                    case "8":
                    case "9":

                        st = 3;
                        break;

                    case "}":
                    {
                        var d = formatString.substr(j, i - j);
                        var n = parseInt(d);

                        if (n + 1 >= arguments.length)
                        {
                            console.error("stringFormat: The parameter {" + n + "} was not provided. Format string:", formatString);
                            return null;
                        }

                        builder.push(arguments[n + 1]);

                        st = 0;
                        j = i + 1;
                        break;
                    }   

                    default:

                        console.error("stringFormat: Pattern error processing string", formatString, "at index", i);
                        return null;
                }
                break;
            }
        }
    }

    if (i > j)
    {
        builder.push(formatString.substr(j, i - j));
    }

    return builder.join("");
}