oxc/no-async-endpoint-handlers Suspicious

What it does

Disallows the use of async functions as Express endpoint handlers.

Why is this bad?

Before v5, Express will not automatically handle Promise rejections from handler functions with your application's error handler. You must instead explicitly pass the rejected promise to next().

const app = express();
app.get("/", (req, res, next) => {
  new Promise((resolve, reject) => {
    return User.findById(req.params.id);
  })
    .then((user) => res.json(user))
    .catch(next);
});

If this is not done, your server will crash with an unhandled promise rejection.

const app = express();
app.get("/", async (req, res) => {
  // Server will crash if User.findById rejects
  const user = await User.findById(req.params.id);
  res.json(user);
});

See Express' Error Handling Guide for more information.

Examples

Examples of incorrect code for this rule:

const app = express();
app.get("/", async (req, res) => {
  const user = await User.findById(req.params.id);
  res.json(user);
});

const router = express.Router();
router.use(async (req, res, next) => {
  const user = await User.findById(req.params.id);
  req.user = user;
  next();
});

const createUser = async (req, res) => {
  const user = await User.create(req.body);
  res.json(user);
};
app.post("/user", createUser);

// Async handlers that are imported will not be detected because each
// file is checked in isolation. This does not trigger the rule, but still
// violates it and _will_ result in server crashes.
const asyncHandler = require("./asyncHandler");
app.get("/async", asyncHandler);

Examples of correct code for this rule:

const app = express();
// not async
app.use((req, res, next) => {
  req.receivedAt = Date.now();
});

app.get("/", (req, res, next) => {
  fs.readFile("/file-does-not-exist", (err, data) => {
    if (err) {
      next(err); // Pass errors to Express.
    } else {
      res.send(data);
    }
  });
});

const asyncHandler = async (req, res) => {
  const user = await User.findById(req.params.id);
  res.json(user);
};
app.get("/user", (req, res, next) => asyncHandler(req, res).catch(next));

Configuration

This rule takes the following configuration:

type NoAsyncEndpointHandlersConfig = {
  /**
   * An array of names that are allowed to be async.
   */
  allowedNames?: string[];
};

References

• Rule Source