Format a string using placeholders

function placeholders()
{
    var str = "Name: {0} Age: {1}";
    String.prototype.format = format;
    cons.innerHTML = str.format("Pesho", 18);

    function format()
    {
        var replaced = this;
        for (var i = 0; i < arguments.length; i++) {
            var regex = new RegExp('\\{'+i+'\\}');
            replaced = replaced.replace(regex,arguments[i]);
        }
        return replaced;
    }
}