Function definition question

Question

Hi all, I am a first time poster, long time Flash user, who is trying to wrap his head around AS3.
When writing functions, I am unclear on on the part that goes inside the parentheses.  For instance, I have see some functions that say:
function XXXXXXX (event:MouseEvent) {
and then some that say:
function XXXXXXX (e:TimerEvent) {
and I think even some that say:
function XXXXXXX (somethingElse:something) {
I get the parts that go after the colon, it is the part before the colon that confuses me.  There seems to be many different posiblities that go before the colon.
How do you know which one, which syntax to use when coding?
By chance they aren't all interchangeable are they?
If not, is there a list that works with the "event:", a different list that works with "e:", etc?
Thanks in advance

Answer 1

what goes before the colon is the variable name.  This is what you use inside the function to refer to the (in this instance) event that is passed in.  This is completely changeable - you could make it gobbledygook:MouseEvent if you wanted to.  Typically best practices state that you should name variables based on their content, so that is why you see event:VideoEvent frequently, and often the shortened version e:VideoEvent.
And, for a little more explanation.
These event parameters (e:MouseEvent) are what is passed when the function is fired from an event listener. (someButton.addEventListener(MouseEvent.CLICK,doClick);)
You don't need to put anything inside of the parentheses if nothing is getting passed into the function.  For example:
function doSomething():void {
trace("something");
This function doesn't need anything in the parentheses, because nothing is getting passed in.  It would be called by a simple doSomething(); in the code.