[FlexJS] more on undefined / non initialised values

[Justin Mclean]

Hi,

So if you run this code on AS
public var s:String;
public var o:Object;
public var i:int;
public var n:Number;
public var b:Boolean;

public function init():void {
    trace(s);
    trace(o);
    trace(i);
    trace(n);
    trace(b);
}

You get:
null
null
0
NaN
false
null

but on JS you get:
undefined
undefined
0
undefined
undefined
undefined

Now with strings, objects and Arrays you can get issues with === and !== as 
they are null on one platform and undefined on an another - as discussed in the 
other thread.

But the issue is worse with Numbers and Booleans as there are additional 
concerns. Performance is also an issue as JS doesn't know what type they are 
and will be slowed down by implicit casting.

For example this code will not do as you expect and say b is true when it is 
not as undefined != false.

var b:Boolean;

if (b == false)
{
  trace(“b is false”);
}
else
{
  trace(“b is true”);
}

Luckily isNaN(undefined) returns true, NaN != undefined so that may cause some 
issues as well.

Thanks,
Justin