MathJax: automatic equation numbering: set counter macro

AMS-setcounter.js

window.MathJax = {
  jax: ["input/TeX", "output/HTML-CSS"], //just some defaults
  extensions: ["tex2jax.js", "MathMenu.js", "MathZoom.js"],
  TeX: {
    extensions: ["AMSmath.js", "AMSsymbols.js"],
    equationNumbers: {
      autoNumber: "AMS"
    }
  },
  AuthorInit: function() {
    MathJax.Hub.Register.StartupHook("TeX AMSmath Ready", function() {
      MathJax.InputJax.TeX.Definitions.Add({
        macros: {
          setCounter: "setCounter"
        }
      }, null, true);
      MathJax.InputJax.TeX.Parse.Augment({
        setCounter: function(name) {
          var num =  parseInt(this.GetArgument(name));
          MathJax.Extension["TeX/AMSmath"].number = num;
        }
      });
    });
  }
};