new Promise(function(resolve){
  setTimeout(function() {
    console.log(1);
    resolve();
  }, 1000);
}).then(function() {
  let nextPromise = new Promise(function(resolve){
    setTimeout(function() {
      console.log(2);
      resolve();
    }, 1000);
  });
  return nextPromise;
}).then(function() {
  let nextPromise = new Promise(function(resolve){
    setTimeout(function() {
      console.log(3);
      resolve();
    }, 1000);
  });
  return nextPromise;
}).then(function() {
   setTimeout(function() {
      console.log(4);
   }, 1000);
});