Do you know what will be the output of this code? Promise.resolve(1) .then((x) => x + 1) .then((x) => { x * 2; }) .then((x) => console.log(x));

Why does a .then() without return pass undefined?

Do you know what will be the output of this code?

JavaScript

Promise.resolve(1)
  .then((x) => x + 1)
  .then((x) => {
    x * 2;
  })
  .then((x) => console.log(x));

Show answer and explanation

The answer is undefined.

The second callback uses braces, so it needs an explicit return. Without one it returns undefined, and that’s what the next .then receives.