Promise.all(): Concurrent Asynchronous Operations

So far, we've sequenced asynchronous tasks one after another. But when tasks are independent, you can run them in parallel with Promise.all(), which “fail-fast” rejects if any input Promise rejects, or resolves with an array of all results.

1. What is Promise.all()?

Promise.all() takes an array of Promises and returns a new Promise that:

• Resolves when all input Promises resolve, with an array of their values.
• Rejects immediately when any input Promise rejects, with that first rejection reason.

2. Fail-Fast Rejection Behavior

If any Promise rejects, Promise.all() immediately rejects with that error.

3. Using Promise.all() with async/await

You can await a Promise.all() inside an async function to run tasks in parallel and then destructure their results.

Exercise: Fetch Multiple Pokémon Concurrently

Instructions:

1. Write an async function fetchPokemonData().
2. Define an array of names (e.g. 'pikachu', 'charizard', 'squirtle', 'invalid').
3. Map names to Promises via fetch('https://pokeapi.co/api/v2/pokemon/'+name) + .json(), checking response.ok.
4. await Promise.all() on that array.
5. On success, log each Pokémon’s name and height.
6. Use try...catch to handle any fetch or JSON errors.
7. Include a finally to signal completion.