thanks a lot. But why did they made it so complex? do we really need
the granularity to differenciate between "undefined", null, 0, "" and
false ?
On Thu, Feb 19, 2009 at 1:51 AM, RobG <rg...@iinet.net.au> wrote:
>
>
>
> On Feb 19, 9:44 am, Alexandre Plennevaux <aplennev...@gmail.com>
> wrote:
>> thanks guys, so if i understand correctly, an unset property, if
>> tested, returns "false". Correct ?
>
> Strictly, no. It returns undefined, which may evaluate to false
> depending on the test, which should be based on the possible values
> and how they should be treated.
>
> If you just want to see if it has some value that is or isn't
> "falsey", use:
>
> if (obj.property) {...}
>
>
> which will evaluate to false where obj.property has one of a number of
> values - undefined, null, NaN, 0 (i.e. the number zero but not the
> string zero), boolean false and so on. If you declare the property
> but don't give it a value, its value is undefined (as in not defined)
> and if evaluated as part of an exrpession, undefined (the special
> undefined value) is returned.
>
> Therefore if you declare it and later want to see if it has been
> assigned a value, the best test is probably:
>
> if (obj.property === undefined) {...}
>
> It's your decision as to which is more appropriate.
>
>
> --
> Rob
