Throw await syntax in Nodejs async express handler is not working

[samislam]

const express = require("express");
const expressAsyncHandler = require("express-async-handler");

const app = express();

const f = async () => {
  return false;
};

app.get(
  "/",
  expressAsyncHandler(async () => {
    throw await f();
  }),
  () => {
    console.log("the bug!");
  }
);

app.use((err, req, res, next) => {
  console.log("caught!", err);
});

app.listen(4000, () => console.log("listening on port 4000..."));

Expected output on the console:

"caught!".

output:

the bug!.

question: Why? Is it a bug in async-express-handler package or is it a normal JavaScript behaviour? what if I want to throw await something inside? how ?

[MiccWan]

@samislam

I think this is an intended design by express.

Although, express.js said that "If you pass anything to the next() function (except the string 'route'), Express regards the current request as being an error and will skip any remaining non-error handling routing and middleware functions.", they actually ignoring any falsy values passed to next().

In your case, f() is returning false and is ignored by express. Instead of false, you may throw an error e.g. new Error('some error message...') or any value that is not falsy.

I'm not the maintainer of express-async-handler by the way and I hope you find this information helpful.

[bergus]

Cross-posted on StackOverflow: Throw await syntax in Nodejs async express handler is not working (with pretty much the same conclusion as @MiccWan).

You may close this issue I think.

[samislam]

Cross-posted on StackOverflow: Throw await syntax in Nodejs async express handler is not working (with pretty much the same conclusion as @MiccWan)

Yes, it's actually me