AS3 Mystery: null, false, 0, “”, NaN
April 2nd, 2009
This week I've been running unit tests and couldn't understand why some of them were failing for no obvious reason. To understand why some expressions evaluated to true when they were supposed to be false. I know that I should be careful with null vs false values, but never could I have imagined that the Number 0 can be equal to an empty String!
I know that php's empty() function is quite permissive, but I though AS3 was much more strict (with strict typing and all). And so I ran a different kind of test, where I checked these values in depth. Here is a table describing my results.
| null | false | 0 | "" | NaN | |
|---|---|---|---|---|---|
| isNaN() | true | ||||
| == "" | true | true | true | ||
| === "" | true | ||||
| == null | true | ||||
| === null | true | ||||
| == 0 | true | true | true | ||
| === 0 | true | ||||
| == false | true | true | true | ||
| === false | true | ||||
| is Number | true | true | |||
| is String | true | ||||
| is Boolean | true | ||||
| is Object | true | true | true | true |
You will notice that NaN is actually a Number and an Object, that 0 == "" == false and that false is actually an Object. There are quite a few surprises in there that will make me appreciate strict comparison.
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