Frame agent override causes TypeError with an XHR request from Dropzone

[mjgiarlo]

My team's been enjoying Cyperful for ironing out kinks in our system specs, and recently we wrote a test of a file upload feature in our application and found that while the spec passes in RSpec, it fails when invoked via Cyperful. In the JavaScript console of Chrome, when we drop a file into the upload dropzone, we see Uncaught TypeError: Illegal invocation:

It appears to be the e.apply(this, n); call in the XHR override within the Cyperful frame agent:

cyperful/frame-agent/index.ts

Line 156 in 67924cb

return originalOpen.apply(this, args);

, just after DropzoneJS attempts to make an XHR request (here). It appears the reference to this is problematic here.

Is this XHR override in the frame agent required? When I comment out the XHR override locally, the tests all pass, for what it's worth. Maybe there's a way to rewrite the override so that the this reference doesn't bomb out? Happy to make changes on my side if you have suggestions.