What happens if a promise completes before then is called?

Question

Let\'s say I have a Promise like this:

var promise = new Promise(function(resolve, reject) {
    // Do some async thing
});
promise.then(functio         


        

Answer 1

As expected: then callback will get called immediately in this case if then was called after promise has already resolved.

It's easy to test:

var promise = new Promise(function(resolve, reject) {
    resolve(123);
});

setTimeout(function() {
  promise.then(function(response) {
      alert(response);
  });
}, 1000)