app.js

var express = require('express');
var bodyParser = require('body-parser'); // middleware for parsing request body.
var app = express();
app.use(bodyParser.text({extended: true}));

var mjAPI = require("mathjax-node/lib/mj-single.js");
mjAPI.start();

app.get('/', function (req, res) {
  mjAPI.typeset({
    math: "\\Gamma(z) = \\int_0^\\infty t^{z-1}",
    format: "TeX",
    svg: true,
    mml: true
  }, function (result) {
    res.send(result);
  });
});

app.post('/', function (req, res) {

  try {
    mjAPI.typeset({
      math: req.body,
      format: "TeX",
      svg: true,
      mml: true
    }, function (result) {
      res.send(result);
    });
  } catch (exception) {
    console.log("A Mathjax exception occured. " + exception);
    mjAPI.start();
    res.send();
  }
});

var server = app.listen(8080, function () {
  var host = server.address().address;
  var port = server.address().port;
  console.log('Server listening at http://%s:%s', host, port);
});