The point of MathJax is so that users can type math the way they are used to—typically TeX syntax, though MathJax also supports AsciiMath and MathML itself—and get nicely typeset output (MathJax has three output formats: MathML, SVG, and HTML+CSS). At most you could say that MathJax's MathML input and HTML+CSS output are no longer needed, but that's not the bulk of the need that MathJax serves. Also:
1. [Input] Even if only targeting MathML output, you still need some way to take the user's TeX input and generate MathML, which is what MathJax provides here. What are the alternatives to MathJax that you have in mind? The closest competitor I'm aware of is KaTeX, and while it is fast when it works, there are still some holes in its support (relative to MathJax). (Another comment in this discussion points out Temml, which indeed looks good: https://temml.orghttps://github.com/ronkok/Temmlhttps://temml.org/docs/en/comparison.html )
(Also, on a lot of these MathML demo pages, selecting and copy-pasting the math produces junk, while with MathJax there's a right-click menu providing the TeX source and also some accessibility options… it seems that accessibility is actually higher with MathJax under certain circumstances at least.)
My main beef with MathJax is how it searches for equation on the entire page and renders it in place instead of using something like a custom element. E.g. in TeXZilla you can write something like:
In my own mathup library I have a similar functionality:
<math-up>x = -b+-sqrt(b^2 - 4ac) / 2a</math-up>
For MathJax to continue staying relevant it should probably do something similar (note that it is not that hard [1]).
As for the output. This is in large part due to the font being used. The default math font for me using firefox on ubuntu is indeed rather ugly. If you want something similar to the TeX output you can simply use the TeX-Gyre font face. In my documentation for mathup[2] I use Libertinus Math, which pairs very nicely with the other font faces on the page (Libertinus and Libertinus Mono). Aside: here is another example of why MathML is a superior target output then HTML+CSS as you actually have control over the font face.
And finally, as for the copy-pasting. You can download numerous browser add-ons that make copy-pasting formulas as easy as MathJax’s. I will admit this is a handy feature of MathJax, and if you want user to be able to copy-paste your expressions while not assuming they will download an add-on to do so, then MathJax is probably your number 1 choice.
2: https://runarberg.github.io/mathup/ - Note, I haven’t updated the software to target the newer MathML Core, so many expressions will not work in Chrome. You should definitely use MathJax over my library.
Thanks for these helpful links. Looking at the Mozilla examples in mobile Safari just now and the MathML rendering is pretty dreadful for almost all of them. It looks like there is still a long way to go.
1. [Input] Even if only targeting MathML output, you still need some way to take the user's TeX input and generate MathML, which is what MathJax provides here. What are the alternatives to MathJax that you have in mind? The closest competitor I'm aware of is KaTeX, and while it is fast when it works, there are still some holes in its support (relative to MathJax). (Another comment in this discussion points out Temml, which indeed looks good: https://temml.org https://github.com/ronkok/Temml https://temml.org/docs/en/comparison.html )
2. [Output] The MathML output rendering in browsers is not yet 100% identical to TeX's typesetting (they're certainly aware of it / thinking of the right things, looking at the mentions of [TEXBOOK] at https://w3c.github.io/mathml-core ), and this may even be intentional. In particular, looking at various MathML demo pages I found online (http://eyeasme.com/Joe/MathML/MathML_browser_test.html https://fred-wang.github.io/MathFonts/mozilla_mathml_test https://www-archive.mozilla.org/projects/mathml/demo/texvsmm... and Temml's useful demo pages: https://temml.org/tests/wiki-tests https://temml.org/tests/latexml-tests https://temml.org/tests/mozilla-tests) it appears that in all three of Chrome/Firefox/Safari the rendering of nested square roots is a bit suboptimal, while Safari has some more serious issues (example 9 of the Mozilla MathML Test looks poor in Safari). But clearly the Igalia (for Chrome) and Mozilla folks have done great work, and it's pretty close, but in the meantime I imagine at least some authors would prefer the more deterministic (across browsers) output of SVG or HTML+CSS.
(Also, on a lot of these MathML demo pages, selecting and copy-pasting the math produces junk, while with MathJax there's a right-click menu providing the TeX source and also some accessibility options… it seems that accessibility is actually higher with MathJax under certain circumstances at least.)