ES 2015 async/await error handling demo (better error stacktraces)

async-error-demo.js

'use strict';

// ==============================================================
// HELPERS
// ==============================================================

// Needed to create a _really_ asynchronous function. A fake asynchronous function (returning "Promise.reject()"
// right away, for example) actually creates a stacktrace.
const wait = delay => new Promise(resolve => setTimeout(() => resolve(), delay));

// Some deeply nested (in the actual call hierarchy) asynchronous function that throws an error.
const fnError = async () => Promise.reject(new Error('Ooohhhh my god, this went wrong!'));


// ==============================================================
// TEST: OPTION #1 with await, try/catch, new Error(err)
// ==============================================================

const fnA1 = async () => {
    await wait(1);
    try {
        await fnA2();
    } catch(err) {
        console.log('Caught an error in fn2 call', new Error(err));
        throw err;
    }
};

const fnA2 = async () => {
    await wait(1);
    try {
        await fnError();
    } catch(err) {
        console.log('Caught an error in fnError call', new Error(err));
        throw err;
    }
};


// ==============================================================
// TEST: OPTION #2 with await, try/catch, WITHOUT new Error(err)
// ==============================================================

const fnB1 = async () => {
    await wait(1);
    try {
        await fnB2();
    } catch(err) {
        console.log('Caught an error in fn2 call', err);
        throw err;
    }
};

const fnB2 = async () => {
    await wait(1);
    try {
        await fnError();
    } catch(err) {
        console.log('Caught an error in fnError call', err);
        throw err;
    }
};


// ==============================================================
// TEST: OPTION #3 with await, WITHOUT try/catch
// ==============================================================

const fnC1 = async () => {
    await wait(1);
    const result = await fnC2();
    return result;
};

const fnC2 = async () => {
    await wait(1);
    const result = await fnError();
    return result;
};


// ==============================================================
// TEST: OPTION #4 (simply return the sub-function's promise)
// ==============================================================

const fnD1 = async () => {
    await wait(1);
    return fnD2();
};

const fnD2 = async () => {
    await wait(1);
    return fnError();
};


// ==============================================================
// RUN DEMOS
// ==============================================================

(async () => {
    console.log('\nOPTION #1 (with await, try/catch), new Error(err))\n');
    await fnA1().catch(console.error);
    console.log('\n\nOPTION #2 (with await, try/catch - WITHOUT new Error(err))\n');
    await fnB1().catch(console.error);
    console.log('\n\nOPTION #3 (with await, no try/catch, WITHOUT new Error(err))\n');
    await fnC1().catch(console.error);
    console.log('\n\nOPTION #4 (simply return the sub-function\'s promise)\n');
    await fnD1().catch(console.error);
})()
.catch(console.log);