CHEGG BACKED DEV

Backend development reference

Node and Express are the runtime and HTTP framework for your API. Topics here cover bootstrapping the app, parsing JSON bodies, and structured logging—everything that runs before a route handler executes. Master this layer first so later routers and controllers plug into a consistent foundation.

Async and await in Express

Matches Async and await in Express: Promises, async controllers, and awaiting Knex in services.

3 topic(s) on this page.

How Promises work in backend code — Basic

Node / Express Async and await in Express
A Promise represents async work that will finish later (database, file, network). Knex queries return promises; Express handlers use async/await to read results cleanly.
Learn: Before async/await, Promises were the standard way to handle async results in Node. Knex still returns a Promise from every query builder chain. Understanding then/catch helps you read older examples; writing new code with async/await is usually clearer in controllers and services.

Supplementary examples

Promise.all for parallel queries

const [users, pastes] = await Promise.all([
  knex("users").select("*"),
  knex("pastes").select("*"),
]);

Course example

// Knex returns a Promise
const promise = knex("users").select("*");

promise
  .then((rows) => console.log(rows))
  .catch((err) => console.error(err));

// Same query with async/await (preferred in controllers/services)
async function listUsers() {
  const rows = await knex("users").select("*");
  return rows;
}

Additional references & examples

How to write async route handlers — Intermediate

Node / Express Async and await in Express
Mark controller functions async and await service/Knex calls. Always forward failures with next(err) so the error middleware can respond.
Learn: Async handlers must forward rejections with `next(err)`—otherwise Express may not invoke your error middleware. Wrapping async functions or using a small `asyncHandler` utility removes repetitive try/catch blocks.

Supplementary examples

asyncHandler wrapper

function asyncHandler(fn) {
  return (req, res, next) => {
    Promise.resolve(fn(req, res, next)).catch(next);
  };
}

router.get("/", asyncHandler(async (req, res) => {
  const rows = await service.list();
  res.json({ data: rows });
}));

Course example

async function create(req, res, next) {
  try {
    const created = await service.create(req.body);
    res.status(201).json({ data: created });
  } catch (err) {
    next(err);
  }
}

Additional references & examples

How to return Promises from services — Intermediate

Node / Express Async and await in Express
Service functions return promises (or async functions that return data). Controllers await them; do not mix callback-style Knex with async/await in the same path.
Learn: Keep Promise-returning database code in services. The controller awaits one or more service calls and maps results to HTTP. If you return knex(...) directly from a service without await inside, the controller still awaits the same Promise—both styles work if errors propagate to next(err).

Supplementary examples

async service function

async function remove(pasteId) {
  const deleted = await knex("pastes").where({ paste_id: pasteId }).del();
  if (!deleted) {
    const err = new Error("Paste not found");
    err.status = 404;
    throw err;
  }
}

Course example

// service — return the Knex promise (or use async/await inside)
function listByUser(userId) {
  return knex("pastes")
    .where({ user_id: userId })
    .orderBy("created_at", "desc");
}

// controller
async function list(req, res, next) {
  try {
    const rows = await service.listByUser(req.params.userId);
    res.json({ data: rows });
  } catch (err) {
    next(err);
  }
}

Additional references & examples