JS | Promises

.md

JavaScript

Async, Await, Try Catch JS (Promises)

AsyncAwaitTryCatchJS.md

AsyncAwaitTryCatch

Handling UnhandledPromiseRejectionWarning

Stacktrace:

This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch().

simpleAsync.js

const fetch = require("node-fetch");

async function fetchUsers() {
  const res = await fetch("https://jsonplaceholder.typicode.com/users");
  const data = await res.json();
  console.log(res.json());
}

fetchUsers();

// Output
// [
//   {
//     id: 1,
//     ...
//   },
//   {..}
//   ...
// ]

simpleTryCatch.js

function thisThrows() {
  throw new Error("Thrown by thisThrows()");
}

try {
  thisThrows();
} catch (error) {
  console.error(error);
} finally {
  console.log("We do clean up here");
}

// Output:
// Error: Thrown from thisThrows()
//   ...stacktrace
// We do clean up here

tryCatchWithPromise.js

async function thisPromiseThrows() {
    throw new Error("Thrown by thisPromiseThrows()");
}

try {
    thisPromiseThrows();
} catch (error) {
    console.error(error);
} finally {
    console.log("We do clean up here");
}

// Output: // Notice the mixed up order of the output plus the UnhandledPromiseRejectionWarning
// We do clean up here
// UnhandledPromiseRejectionWarning: Error: Thrown from thisPromiseThrows()


// Solution 1
async function thisPromiseThrows() {
    throw new Error("Thrown by thisPromiseThrows()");
}

async function run() {
    try {
        await thisPromiseThrows(); // <- Notice the await keyword here
    } catch (error) {
        console.error(error);
    } finally {
        console.log("We do clean up here");
    }
};

run();

// Solution 2
async function thisPromiseThrows() {
    throw new Error("Thrown by thisPromiseThrows()");
}

thisPromiseThrows()
    .catch(console.error)
    .then(() => console.log("We do clean up here"));

// 

Target: Novice in JS

Source: https://itnext.io/error-handling-with-async-await-in-js-26c3f20bc06a

Opinion: Use Solution 1 since it's clear.