Promises within a chain in JavaScript

Functions within a chain can also return promises. In this case, the result of this promise will fall into the next then:

javascriptpromise.then(
  function(result) {
    return result + '1';
  }
).then(
  function(result) {
    return new Promise(function(resolve) {
      resolve(result + '2'); // this result will fall into the next then
    });
  }
).then(
  function(result) {
    return result + '3';
  }
).then(
  function(result) {
    console.log(result); // shows 'string123'
  }
);