Re: [FlexJS] more on undefined / non initialised values

[Josh Tynjala]

Good points. I'm all for initializing more than we do now. Even if we don't
achieve parity with all types, Booleans should definitely default to false
and Numbers to NaN, if they aren't explicitly initialized with a value, in
my opinion.

- Josh

On Jun 3, 2017 7:27 PM, "Justin Mclean" <jus...@classsoftware.com> wrote:

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