I have loaded MathJax by putting into the header of an HTML file,
<script type="text/javascript"
src="https://cdn.mathjax.org/mathjax/latest/MathJax.js?config=TeX-AMS-MML_HTMLorMML">
</script>
It clearly seems to be loading the "latest" version. However, when I google what the latest version is, it's 3.x. However, when I try to use a function that is in 3.x which is not in 2.x, MathJax.typeset(), I get an error that this is not recognized.
When I try to pop open a developer console and enter MathJax --version it doesn't recognize this. So how can I confirm which version is being loaded into the page?
If you open the URL
https://cdn.mathjax.org/mathjax/latest/MathJax.js?config=TeX-AMS-MML_HTMLorMML
in a browser, you get Javascript code which contains the following lines
(function () {
var newMathJax = 'https://cdnjs.cloudflare.com/ajax/libs/mathjax/2.7.1/MathJax.js';
var oldMathJax = 'cdn.mathjax.org/mathjax/latest/MathJax.js';
...
//
// Issue a console warning
//
console.warn('WARNING: cdn.mathjax.org has been retired.
Check https://www.mathjax.org/cdn-shutting-down/ for migration tips.')
So, you might want to have a look at
https://www.mathjax.org/cdn-shutting-down
Upgrade from v2 to v3 is described in