Callback hell

callback-hell.js

function process(callback) {
  var name = "john";
  if (name==="john") {
    callback(null, "My name is john");
  } else {
    callback("I am not john");
  }
}

process(function(error, message) {
  if (error) {
    console.error(error);
  } else {
    console.log(message);
  }
})

Check out the corresponding Async-Await example -
https://gist.github.com/warrenca/9f11ceef456a3603d42d4c23b359e409 or in babel