Currently, the Stack Exchange sites use MathJax v2 (see Which Stack Exchange sites use MathJax? for list of sites) which slowly becomes obsolete as new version 3.0.0 is in the last beta. Since MathJax v3 is a major rewrite from v2, I would like to bring up this discussion on whether or when, there is a plan to switch to this version, and also consider alternatives.
MathJax version 3 beta 4 has been announced on May 21, 2019, and it the final planned beta version before release before official 3.0 release. However they changed it from version v2 quite a lot (see Upgrading from v2 to v3), so it is not a simple drop-in replacement. Also as noted by Davide Cervone in my previous mathematics meta post Switch to MathJax version 3?, there are still some critical features that are not yet (as of 11/23/2019) implemented, such as automatic line breaking (and preview editor updates are mentioned as well).
For the list of new features see http://docs.mathjax.org/en/latest/upgrading/whats-new-3.0.html.
KaTeX (see the official KaTeX site) seems to be faster alternative to MathJax, see for example KaTeX and MathJax Comparison Demo, BUT (!!) note that is demo compares against MathJax version 2.7.2, and might not be accurate as MathJax v3 also improved performance (some more up to date comparison would be needed).
However I can't help but it seems that MathJax renders prettier equations, but it seems to be that the performance should be more important. Also, one thing I have noticed, the KaTeX (or at least its examples) do not offer the context menu (for example to view the equation source).
KaTeX has been already considered on this site in past, see for example these:
- A MathJax alternative from Khan Academy (Sep 15, 2014)
- KaTeX instead of Mathjax (Sep 15, 2017)
- A contender for MathJax? (Sep 16, 2014)
However, it seems lots (if not all) of the features that were missing/objected then are now implemented, you can try the KaTeX renderer on https://stackedit.io/app#, so I believe it is worth re-evaluating as of 2019. See also Supported KaTeX Functions.
Update for 2021: This site has a comparison of MathJax 2.7 vs Katex vs MathJax 3. MathJax 3 speeds seem comparable to Katex though v2.7 is significantly slower.