[Dojo-interest] How to debug "This deferred has already been resolved" errors

[Jean-Pierre Bergamin]

Hello dojo users

I'm always having a hard time to debug programmatic errors in deferred functions. Let's have a look at an example, where myPane is a ContentPane:

myPane.set("onDownloadError", function(err) {

    var myNull;

    myNull.get("foo");

    return err.message;

});

myPane.set("href", "some/url");

There is a bad bug in the "onDownloadError" function. In the console I see:

8<------------------------------------------------------------------- 

Error
arguments: undefined
get stack: function getter() { [native code] }
message: "This deferred has already been resolved"
set stack: function setter() { [native code] }
type: undefined
__proto__: ErrorPrototype

dojo.Deferred.reject.errback    Deferred.js:216
dojo.Deferred.reject.errback    Deferred.js:216
notify    Deferred.js:186
complete  Deferred.js:162
dojo.Deferred.reject.errback    Deferred.js:213
notify   Deferred.js:186
complete    Deferred.js:162
dojo.Deferred.resolve.callback    Deferred.js:203
notify   Deferred.js:184
complete   Deferred.js:162
dojo.Deferred.resolve.callback    Deferred.js:203
_resHandle    xhr.js:620
func    xhr.js:506
_watchInFlight    xhr.js:525

8<-------------------------------------------------------------------

There is no actual trace to the function that cause this error.

How do I actually find out that this error comes from the onDownloadError handler? What's a good way to debug such errors?

Best regards,

James