Different scenarios of ES6 promises and async/await catching and swallowing Errors

typescript_promises_swallows_errors.ts

"use strict";


function doThrow() {
    throw new Error("an error!");
}

function doAsyncSuccess() : Promise<void> {
    return new Promise<void>((resolve, reject) => {
        setTimeout(() => resolve(), 10);
    });
}

async function doAsyncFail() : Promise<void> {
    return new Promise<void>((resolve, reject) => {
        setTimeout(() => doThrow(), 10);
    });
}

function doAsyncReject() : Promise<void> {
    return new Promise<void>((resolve, reject) => {
        setTimeout(() => reject('promise rejected'), 10);
    });
}

async function run() {
    await doAsyncSuccess();
    await doAsyncFail();
}

async function runAndThrow() {
    await doAsyncSuccess();
    throw new Error("a sync error in async function!");
}

async function runAndReject() {
    await doAsyncSucces();
    await doAsyncReject();
}


doAsyncSuccess().then(()=> doAsyncFail());
//     throw new Error("an error!");
//     ^
//
//   Error: an error!


doAsyncSuccess().then(()=> {throw new Error('error thrown in .then()')});
// NO OUTPUT


run();
//     throw new Error("an error!");
//     ^
//
//   Error: an error!


runAndThrow();
// NO OUTPUT


run().catch(reason => console.log('caught error: ' + reason));
//     throw new Error("an error!");
//     ^
//
//   Error: an error!


runAndThrow().catch(reason => console.log('caught error: ' + reason));
// caught error: Error: a sync error in async function!


runAndReject();
// NO OUTPUT


runAndReject().catch(reason => console.log('caught error: ' + reason)); 
// caught error: promise rejected