javascript - access prototype function from this -

i trying fix javascript uses functions , prototype functions. reason prototype function always undefined when try access , can't figure out why.

here simple example of i'm trying do. basically, want reference _open prototype within original container function declaration using this.

container();  function container() {     alert(this._open); }  container.prototype._open = function() {     alert("hey"); } 

you can see in fiddle alerts "undefined." this question , this question both show examples of people doing this. why keep getting undefined?

three things:

• use new container(); instead of container();.
• move new container(); line after prototype additions.
• call this._open(); instead of alert(this._open); execute function.

so code should this:

function container() {     this._open(); }    container.prototype._open = function() {     alert('open'); } new container(); 

hope helps.