AI solution for JavaScript Quiz on BFE.dev
23. Promise.all()

The code will output the following by console.log:

// Output:

[]
[1, 2, 3, 4]
error

Explanation:

The code uses Promise.all method to combine multiple promises into a single promise which is resolved when all the promises are resolved or rejected when any one of the promises rejects.

In the first Promise.all, an empty array is passed, so the promise is resolved immediately, and then callback is executed with an empty array, which is logged to the console.

In the second Promise.all, an array with values 1, 2, Promise.resolve(3), Promise.resolve(4) is passed. The Promise.resolve is used to wrap non-promise values into promises. Since all the promises in the array resolve successfully, the then callback is executed with an array containing all the resolved values [1, 2, 3, 4] which is logged to the console.

In the third Promise.all, an array with values 1, 2, Promise.resolve(3), Promise.reject('error') is passed. The Promise.reject is used to create a promise that always rejects with the specified value. Since one of the promises in the array rejects with the reason 'error', the catch callback is executed with the error message 'error', which is logged to the console.