[Tutor] about global definition

[alan.gauld@freenet.co.uk]

>>I have a code here. I understand i can not draw lines without the
>>global definition of lastX and lastY. But still confused by its use.
>>when should we use global definition?

If you don't use classes then you will need to use global variables
any time you want to pass information between functions and the
functions have a predetermined interface that precludes making the
data parameters. Thus in your case the callback click(event) 
can only take the one parameter, event so you must use 
global variables.

Similarly you need to use globals where you need to 
maintain state between function calls (even of the 
same function)

Otherwisde you should be able to avoid globals.

Using OOP allows you to  hide the global functions 
inside an object which solves both of the above problems.

HTH,

Alan G.