is there any way to create a javascript function like element.function(options)?

Question

I want to create a JavaScript function that works like,

element.mycustomfunction(options);

I know how to do this with jquery but I don't know how to do this with pure JavaScript.

Here is what I have did in my code.

var elm = document.getElementById('someid');

I want do this,

elm.mycustomfunction(options_object);

I have tried,

(function(){
      HTMLElement.prototype.mycustomfunction = function(options){
            console.log( options );
      }
})();

but it doesn't console anything. Is there something what I'm missing?

Thanks in Advance