The answer: `1`, and then `undefined`.

```js run
alert( alert(1) && alert(2) );
```

The call to `alert` returns `undefined` (it just shows a message, so there's no meaningful return).

Because of that, `&&` evaluates the left operand (outputs `1`), and immediately stops, because `undefined` is a falsy value. And `&&` looks for a falsy value and returns it, so it's done.