Throw await syntax in Nodejs async express handler is not working-CodePudding

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 ?

CodePudding user response：

Your problem is that you're throwing the value false. This doesn't fit into nodejs' callback conventions (and by extension, express error handling), which requires the err parameter to get a truthy value to be considered an error. A much simpler way to reproduce the issue:

app.get(
  "/",
  (req, res, next) => {
    Promise.reject(false).catch(next);
    // or even just:
    next(false);
  },
  () => {
    console.log("the bug!");
  }
);

So just don't do that! Always throw an Error, not a string, not something else, and this principle also holds for promise rejections.