The tagFormat extension provides the ability to customize the format of the equation tags and automatic equation numbers. You do this by providing functions in the tagFormat object of the tex block of your MathJax configuration. The functions you can provide are listed in the TagFormat Options section.

For example,

MathJax = {
  section: 1,
  tex: {
    tagFormat: {
      number: (n) => MathJax.section + '.' + n,
      id: (n) => 'eqn-id-' + n

arranges for automatic equation numbers to be of the form 1.n, and uses ids of the form eqn-id-1.n as the id attribute of the tags within the web page. This example uses the modern function notation (using =>), but you could also use function (n) {return ...}.

This extension is already loaded in all the components that include the TeX input jax, other than input/tex-base. To load the tagFormat extension explicitly (when using input/tex-base for example), add '[tex]/tagFormat' to the load array of the loader block of your MathJax configuration, and add 'tagFormat' to the packages array of the tex block.

window.MathJax = {
  loader: {load: ['[tex]/tagFormat']},
  tex: {packages: {'[+]': ['tagFormat']}}