JavaScript exceptions with compiled GWT code

Question

During compilation of a GWT class I got some compiler exception. I filed a bug report for that here: http://code.google.com/p/google-web-toolkit/issues/detail?id=6623

Now I found how to make it compile anyway, by using "draftCompile". However, the generated JavaScript code doesn't work when executed.

The Java source files are available from the bug tracker, and the compiled project is here: http://clientssh1.rbg.informatik.tu-darmstadt.de:9000/war/Gwittest.html

The error is: (Chrome) "Uncaught TypeError: Cannot read property 'testpackage_shared_ship_Level_boards' of null". In Firefox its another error.

The code works in Dev Mode (from Eclipse).

How do I work around this error? Is it related to the compilation/optimization bug? How do I work around it? If it is a bug in and of itself, I should report this too, no?

Edit: the class in question is here: https://gist.github.com/1139147

My only advice will be to compile it with -style PRETTY and try to find where exactly is the problem. I've recently had a problem with the same symptoms (code.google.com/p/google-web-toolkit/issues/detail?id=6579), the only way how to solve it, is to compare compiled Js vs source Java code, to find out where compiler screwed up (btw, when i tried your app in latest firefox it showed a totally different error [17:35:46.422] this$static is null @ clientssh1.rbg.informatik.tu-darmstadt.de:9000/war/gwittest/…) — jusio
– jusio, Commented Aug 9, 2011 at 15:39

JGWeissman · Accepted Answer · 2011-08-11 17:34:08Z

2

The error sounds like the compiled javascript contains code like:

null.testpackage_shared_ship_Level_boards

This would happen if the GWT optimizer believes that your variable of type "Level" which has its field "boards" read, must be null. The optimizer is usually right about that.

So, an approach is to: Compile the code into human readable javascript (-style pretty). Get the javascript error and find the line that caused it. Find the corresponding line your Java source, and trace back where the value of your variable comes from. You will likely find that the variable was not initialized.

answered Aug 11, 2011 at 17:34

JGWeissman

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4 Comments

Janus Troelsen Over a year ago

It is already human readable. You can see the source in the bug report. The optimizer is disabled. It works in development mode.

Paŭlo Ebermann Over a year ago

@user309483: As you accepted this answer, and I can't see how it would help, could you describe how you found the problem in your case?

Janus Troelsen Over a year ago

@Paulo: Well, I figure it was a GWT compiler bug. I solved the problem by running more code server-side (i.e. not GWT compiled)... This answer showed effort and I accept it for confirming my suspicion that the GWT compiler has issues. Also, I didn't wanna get my acceptance quota too low, as I think it will prevent people from answering my questions. Sorry. Note that I had this problem with GWT 2.3.0, they might have fixed whatever caused it.

Glen Pierce Over a year ago

You can answer your own question.

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