Why would enabling coverage from Blanket.js cause click trigger to activate twice?

Question

I have a set of QUnit tests that run and pass on their own without any problems. However, when I recently added Blanket.js to measure javascript code coverage to help find the gaps in my testing, and all of a sudden I had several tests failing. Sprinkling in some alerts to help me locate what was happening. I found that all of my failing tests were ones using click events on functions that toggle between states. These tests were being toggled twice. I've looked into what would could cause double activation of the trigger, but in my code the functions aren't bound twice and I'm only including my javascript file once in the header.

I did notice in Firebug Blanket.js makes a GET request to the script I am testing against. Could the GET request be binding functions a second time or are there any other causes to this double activation?

Answer 1

There's a lot going on under the hood of blanket. From what I can tell, it is essentially evaluating the code you tell it to. So anything that would just "run" will be evaluated once by loading in the DOM, and again when blanket evaluates it.

Answer 2

Because Blanket will load this page scripts matched pattern in data-cover-only again to analayse script coverage, so that all your scripts executed a second time, which might bind your click event twice.

You can see it in the network pannel in Chrome Dev tools, and you will see requests like: