unhandled-rejections-1.md

Use Case #unhandled-rejections-1

Name: Unhandled Rejections: Our current heuristic can be problematic with async functions

Eula is writing regular code with an async function waiting for multiple things and is getting a weird warning.

What happens

async function foo() {
    var p1 = getSomeApi();
    var p2 = getSomeOther();
    await p1;
    // if p2 rejects - it will emit an unhandled rejection
    await p2; // although it is awaited here
}

Here, she is getting an unhandled rejection - she can write the code with a Promise.all that doesn't have that problem.

Why it happens

Because unhandled rejection detection detects promises that reject without a handler attached within a microtick.

What can we maybe do better

Ideally, I think we want to emit an unhandledRejection here (since if p1 rejects the error for p2 is ignored). However, we should consider being less confusing for users about it.

For example a warning for creating multiple promises and then only awaiting a subset of them - if that works.