Promise Error Model

asyncawait.js

'use strict';

const mockClient = {};

// The Promise model groups unintentional errors with errors into the same
// try/catch mechanism.
//
// In most typed languages this is fine because the catch clause gives you some
// flexibility to catch only the errors you are interested in. JS gives you a
// catch all, which makes it hard to distinguish the errors.

async function doStuff() {
    let rand = Math.random();
    let x;

    if (rand > 0.7) {
        // throws a TypeError
        // imagine this leaks a socket underneath the hood.
        // $ echo $? => ?
        mockClient.call();
    } else if (rand > 0.3) {
        // return error to be handled
        // $ echo $? => ?
        throw new Error('handle me!');
    }
    // happy path
    // $ echo $? => 0
    return 'success';
}


(async function() {
    try {
        const msg = await doStuff();
        console.log('completed!', msg);
    } catch (e) {
        // How do I tell which one is a ReferenceError and which one is my
        // error? I only want to rethrow one of them. Becomes more difficult
        // when you are 10 layers deep into an async function call.
        throw e;
    }
}());