Calculator with multiple result value callback

calc_client.js

var Calculator = require('./calc'); // considering we named the Calculator file 'calc.js' and it's on the same dir.

Calculator.add(1, 2, function (err, data) {

  if (err) {
    console.error('something went wrong', err);
  } else {
    console.log('the sum is', data);
  }
});

calc_non_evented.js

var Calculator = {

  // performs the complex computation of summing two integers :P
  // returns 'error' and 'data'.
  add : function (a, b, callback) {
    try {
      
      // we need the 'undefined' here since data is our second parameter.
      callback(undefined, parseInt(a, 10) + parseInt(b, 10));
    } catch (e) {

      // we don't need the undefined param here but we'll add it for completion.
      callback(e, undefined);
    } 
  }
};

// export the Calculator object
module.exports = Calculator;