#350 Promise Chain Output

easy
javascript
promises

What will be the order of the following code:

Promise.resolve(1)
  .then(() => 2)
  .then(3)
  .then((value) => value * 3)
  .then(Promise.resolve(4))
  .then(console.log);

The output will be: 6

  1. Promise.resolve(1) → Initial value is 1
  2. .then(() => 2) → Returns 2
  3. .then(3) → Ignored because 3 is not a function, passes previous value 2
  4. .then((value) => value * 3) → 2 * 3 = 6
  5. .then(Promise.resolve(4)) → Ignored because it's not a function, passes previous value 6
  6. .then(console.log) → Prints 6

Key points:

  • If .then() receives a non-function (like 3 or Promise.resolve(4)), it ignores that handler and passes the previous value through
  • Only function handlers are executed in the chain