I was reading this article on promise chaining : https://javascript.info/promise-chaining . Couldn't understand how Javascript runtime decides if it has to transform result into a Promise or not when Promise chaining is involved. Referring the code below Code 1 returns a integer but Javascript has to return a promise. Code 2 returns a Promise and Javascript can return the same promise

Queries:

1. How does Javascript runtime convert the integer to Promise in code 1?
2. How does the Javascript runtime know it has to return the same Promise in code 2?

#################################  Code1  ####################################################
new Promise(function(resolve, reject) {

  setTimeout(() => resolve(1), 1000); // (*)

}).then(function(result) { // (**)

  alert(result); // 1
  return result * 2;

}).then(function(result) { // (***)

  alert(result); // 2
  return result * 2;

})


########################################### Code2 ########################################

new Promise(function(resolve, reject) {

  setTimeout(() => resolve(1), 1000);

}).then(function(result) {

  alert(result); // 1

  return new Promise((resolve, reject) => { // (*)
    setTimeout(() => resolve(result * 2), 1000);
  });

}).then(function(result) { // (**)

  alert(result); // 2

  return new Promise((resolve, reject) => {
    setTimeout(() => resolve(result * 2), 1000);
  });

})