Can't get width / height of an object

Hello,

I draw a rectangle on the stage, converted it to a symbol and added a onclick function just for testing purposes - I want to get the width / or height of that rectangle:

var test = this.width;

alert(test);

But the alert window just says "undefined".

(I tried to use some other code for var test but it wont work.

How will I get it to work as intended? Can anyone help?