Question

I need something like so

function updateRender(ClassName){
   if(!(this.currentRender instanceof ClassName)){
         doPreprocessing();
         this.currentRender = new ClassName();
         doPostProcessing();
   }
}

So I would be able to call updateRender with a new render object, which can be different type.

updateRender( SolidRender );
updateRender( HollowRender );
updateRender( HollowRender ); //does nothing because currentRender is HollowRender

Answer 1

You’ve already got your answer in the comments, so this is just an FYI:

You’re using this.currentRender, which – if the function is in the global scope – will refer to a variable the global scope. I.e. to the window object of the browser. And putting things in global scope is very rarely a good idea.

Technically, you should put all your code in a single namespace or even inside a function that’s invoked immediately so it doesn’t pollute the global scope. However, you can start by simply getting the currentRender variable out of the global scope by doing this:

var updateRender = (function () {
    var currentRender = null;

    return function (klass) {
        doPreprocessing();
        currentRender = new klass();
        doPostProcessing();
    };

}());

the updateRender function will still be in the global scope, but at least the currentRender variable is safely hidden inside a closure, so only updateRender can change it (aka privileged access).

As for using klass instead of Class, that’s entirely up to you. Using klass is just a common way of getting around the “class is a keyword” problem in Ruby.