I use this little helper in my underground lab:

    function template(str,data){
        for(var i in data){
            str=str.replace(new RegExp("{("+i+")}","g"),data[i])
        }
        return str
    }

It can be used with arrays and object literals as well:

    txt = template('hello {name}!',{name:'Jen'})

    txt = template('days: {0}, {1} and {2}',['mon','tue','wed'])

GPL and WTFPL just in case.

* Looks coincidentally similar to Fuchs'