fix: fix running tests in IE9

[devoto13]

So the symptom is that after Karma page is loaded in IE9 the tests don't run and Karma is stuck at the "starting" step. Reloading the page once or twice makes IE9 connect to the server and tests pass successfully.

After an "exciting" debugging session I figured out that the problem is that on the first load (and sometimes after the page reload) io variable, which should be set by the socket.io.js script is undefined. It looks like IE9 silently stops executing socket.io.js script somewhere midway and switches to the next script causing the io variable to be undefined. I assume it hits some limit or threshold or whatnot. Couldn't find much information on the Internet, besides people experiencing similar issues when loading e.g. unminified jQuery and their own code firing before the $ variable is available. No good solutions found.

Checking the socket.io.js contents, I have noticed that v2 served the minified client script on that path, while v3 now serves the unminified code. Presumably the huge script size is what causing IE9 to choke. Switching back to the minified socket.io client bundle allows tests to pass in IE9.

With the fix, tests passed 5 times in a row, while without it they fail every time, so I assume it does resolve the problem.

Fixes #3665

[karmarunnerbot]

✅ Build karma 569 completed (commit f7d1d1e982 by @devoto13)

[karmarunnerbot]

✅ Build karma 568 completed (commit f7d1d1e982 by @devoto13)

[karmarunnerbot]

✅ Build karma 570 completed (commit b70cec5e82 by @devoto13)

[karmarunnerbot]

✅ Build karma 569 completed (commit b70cec5e82 by @devoto13)

[johnjbarton]

Oh! Based on the fails we saw I thought this was some use of an ES feature by socket-io that IE9 did not support. Good work!

[karmarunnerbot]

🎉 This PR is included in version 6.3.2 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

Your semantic-release bot 📦🚀

[jginsburgn]

How did you debug IE?

[devoto13]

@jginsburgn I logged in to the https://browserstack.com used by Karma, got my user name and access key under ACCESS KEY. Then I added something like below at the top of the test/client/karma.conf.js file and commented out all launchers except the one I want to debug:

process.env.TRAVIS = '1'
process.env.BROWSER_STACK_USERNAME = 'foo'
process.env.BROWSER_STACK_ACCESS_KEY = 'bar'

Then I ran npm run test:client as usual, went back to https://browserstack.com, and found my running job. There is a Start interactive session or something button there, which allows you to tap into a VM, open IE's developer tools and look into what is going on.

[jginsburgn]

Thanks for that! I need to get up to speed on this in order to be better prepared for debugging IE issues that might happen.