test/index.html

<!DOCTYPE html>
<html>
<head>
  <meta charset="utf-8" />
  <style>
    textarea {
      width: 49%;
      height: 400px;
      float: left;
    }
  </style>
</head>
<body>
  <textarea id="code"></textarea>
  <textarea id="result"></textarea><br/>
  <button id="eval">eval</button>
  <script src="../dist/Mason.min.js"></script>
  <script>
    document.getElementById("eval").onclick = function() {
      var code = document.getElementById("code").value;
      var result;

      var env = new window.Mason.Environment();
      env.def("AUTHOR", "Gizeta");
      env.def("TEAM", "Five African");
      env.def("PRINT", function(msg) {
        console.log(msg);
        return msg;
      });

      try {
        result = window.Mason.Execute(code, env);
      } catch (e) {
        result = e.message;
      }
      document.getElementById("result").value = result;
    };
  </script>
</body>
</html>