Update data and use it in real time in Javascript

I want to build a "reader" application for language learning in which the user would highlight the words they wish to learn. I'm using node.js and express

Example here : https://jsfiddle.net/qjttk7xb/3/

  words.forEach(function(word) {
    word.onclick = function() {
      if (word.className == "clicked") {
        word.className = 'notclicked';
      }
      if (word.className == "onmouse") {
        word.className = 'clicked';
      }

I will build a database including every words the user has clicked/highlighted.

What is the best method (module) to update a database in real time?

For example if a user clicks on a word but clicks on it a second time to unhighlight it, I want to update the database in real time.

via Mica Ménard