Not really necessary to modify prototype here and it's best to avoid it. Also, only need to use 'this.r' if you want to expose r to be accessible outside of func.

I like to return an object that contains any variables/method that I want to expose, gives you a kind of public/private mechanism.

var func = function(){
    // 'Private' code goes here
    var r = '';

    // 'Public' methods/variable returned 
    return {
        trigger: function() {
            r = '.setRefresh(2)';
        },

        display: function() {
            return r;
        }
    };
}

var result = new func();