I am a javascript beginner. I do not what this code
mean? Plz explain to me.

'-------------------------------
var key;
if (window.event)
key = window.event.keyCode;
'-----------------------------
what i do not understand is this line:
if (window.event)

Is it in javascript everytime an object is put inside
if syntax

example:
if(object)

Is this used to check whether the object exist or not?
Am I correct?