Fix MathJax font override, avoid double initialization

[bollwyvl]

References

• maybe roll back some ignored issues on Improve examples #14726
• downstream
  • noted on [0.2.0] Update for removed out-of-band MathJax assets jupyterlite/jupyterlite#1192
  • started on Cleanup Mathjax jupyterlite/jupyterlite#1193 by @jtpio

Code changes

• make the overload of TeXFont.defaultFonts static
• move inner contents of protected _ensureInitialized to a Private namespace
  • use a PromiseDelegate to avoid race initilization conditions
  • load all used named MathJax imports in parallel
• remove example 404 ignores
• use font-display: swap to reduce FLOUC

  • tried some preload, etc. but the no-cache setting makes that... worse, and while loading Zero might be a win, it's hard to anticipate the rest...

User-facing changes

• .woff fonts should no longer be downloaded twice from the default URL ({window.location}/js/output/chtml/)
• multiple calls to typeset should not be able to enter the async init code twice

Backwards-incompatible changes

• n/a

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[bollwyvl]

this was the actual important thing

[bollwyvl]

Presumably the example test passed: certainly not seeing the issue locally any longer. Not sure what the story is on the other UI tests.

[jtpio]

Nice, thanks!

I switched the label from enhancement to bug as this looks more like an issue with the current logic.

Also this can likely be backported to 4.0.x.

[jtpio]

Yeah these ignored error were suggesting something was not correct.

[jtpio]

Thanks!

[jtpio]

@meeseeksdev please backport to 4.0.x

[lumberbot-app]

Owee, I'm MrMeeseeks, Look at me.

There seem to be a conflict, please backport manually. Here are approximate instructions:

1. Checkout backport branch and update it.

git checkout 4.0.x
git pull

2. Cherry pick the first parent branch of the this PR on top of the older branch:

git cherry-pick -x -m1 3c3c65ae03a758c620d8dd19678cb891d6bf0f20

3. You will likely have some merge/cherry-pick conflict here, fix them and commit:

git commit -am 'Backport PR #15230: Fix MathJax font override, avoid double initialization'

4. Push to a named branch:

git push YOURFORK 4.0.x:auto-backport-of-pr-15230-on-4.0.x

5. Create a PR against branch 4.0.x, I would have named this PR:

"Backport PR #15230 on branch 4.0.x (Fix MathJax font override, avoid double initialization)"

And apply the correct labels and milestones.

Congratulations — you did some good work! Hopefully your backport PR will be tested by the continuous integration and merged soon!

Remember to remove the Still Needs Manual Backport label once the PR gets merged.

If these instructions are inaccurate, feel free to suggest an improvement.

[bollwyvl]

I'll take a look at the manual backport when i get a chance.