"Assertion Failed" unwrapping event

[keithamus]

Abstract

I seem unable to simply instantiate an Event and dispatch it. Firefox throws an "Assertion Failed" error. This works fine in Chrome however (where I assume the ShadowDOM Polyfill is an effective no-op as Chrome already implements Shadow DOM).

Detail

I have polymer loaded, but I'm trying to manually instantiate a MouseEvent, and dispatch it to a regular DOM element - not involving Polymer. Because dispatchEvent and all of the event constructors have been overwritten, it goes through Polymer code.

I have a reduced test case available here.

document.createEvent('MouseEvent') creates me a GenericEvent from the ShadowDOM (see ShadowDOM events.js:L508-533. The problem seems to be dispatching the event, where an assertion fails in unwrap. The stack looks something like:

• throw new Error('Assertion failed'); (ShadowDOM wrapper.js:L33)
  • (from assert()) (ShadowDOM wrapper.js:L31-34)
• isWrapper(event) (ShadowDOM wrapper.js:L326)
  • (from isWrapper()) (ShadowDOM wrapper.js:L279-287)
  • (from unwrap()) (ShadowDOM wrapper.js:L323-328)
• unwrap(event) (ShadowDOM:L763)
  • (from dispatchEvent(event)) (ShadowDOM:L752-788).

The conclusion of this is that the GenericEvent function does not return instances of the wrappers.* constructors - although I am sure the issue is more nuanced.

[arv]

The issue is with document.body which cannot be wrapped due to this Safari bug: https://bugs.webkit.org/show_bug.cgi?id=122018

If you change it to document.querySelector('body').dispatchEvent it works: http://jsbin.com/gipunuhu/1/

Also, you might want to use new MouseEvent in the future to skip that ugly initMouseEvent crap: http://jsbin.com/gipunuhu/3/edit

[keithamus]

Sorry - the document.body element is actually a red herring in this case. The element I was dispatching the event on was hanging off of my custom elements $ property - but I can't seem to reproduce now. I'll re-open if I can