You have probably been linked to this page from a
JavaScript
License Web Labels page to get the source code to a MathJax file,
tex-svg.js
.
The official instructions for obtaining the MathJax source code are here.
We have also made the source code to a snapshot of MathJax, with included dependencies, available. It is at
this link (206 MB in total).
Extract the file and follow the instructions in the README
file to build the MathJax file.