Hi, mfd
As another datapoint: the Obj-C category `NSObject+NSJSON` treats nulls
as a separate object type: `NSNull`, and all instances are
`NSNull.null`. Instances of JS's undefined is represented with the
equivalent of Java's `null`: `nil`. This is only possible because of
Objective-C's loose typing, and will not transliterate into Java.
Amongst my unsolicited opinions are these:
* code which changes behaviours based on a difference between
`undefined` and `null` should be avoided. Better yet, it should be
shunned or sent for re-education.
* checking if a key exists if different to checking if the value is
`null`. JSONObject has a method `has` which does this. Javans almost
never use the `Map.containsKey`, but if we really need to distinguish
between JS `null` and `undefined`, then we should be using this more.
The usual disclaimers here: purity v pragmatism, refactoring/rewriting
takes time, the wrong-end-of-the-stick etc
- James
On 5/23/14, 1:28 AM, Nick Alexander wrote:
Hi m-f-d,
Just a friendly reminder that JSONObject.optString doesn't do what you
think it does. For terrible reasons documented at [1], if o =
{'key':null}, then
JSONObject(o).optString("key") == "null"
and
JSONObject(o).optString("key", null) == "null"
That's right. I discovered a few places in Fennec where
NativeJSObject does a different thing [2], and then started to look at
our use of optString, and it's not pretty. Way too many uses to audit
:( So instead of trying to fix, I'm trying to educate instead. Be
careful when passing null from JS to Java!
We could try to make NativeJSObject do the right thing, but we have
already gone quite far down the path of NativeJSObject is a drop-in
replacement for JSONObject; I don't think we can go back. And
converting between the two conventions is as hard as auditing all
current uses, amortized over time.
Nick
[1] http://stackoverflow.com/a/23377941
[2] https://bugzilla.mozilla.org/show_bug.cgi?id=1014965
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