Async - Await JavaScript: unable to catch error details from an Error object

Question

In my Node Express JS web app, I have the following function chain where the subsequent api function tries to call the service function and catch the error thrown from the service function.

In FWBDataExtracService.js

const FWBDataExtracService = {
    getFWBData: async () => {
        ... ...
        // Check if .tabledata exists; If not, throw an error to be caught in the calling function.
        if ($('.tabledata1').length == 0) {
            console.error("DOM element .tabledata not found on the page.");
            throw new Error("DOM element .tabledata not found on the page.");
        }
        ... ...
    }
}

In api.js, the router function is trying to call the FWBDataExtracService.getFWBData function and then catching the error.

const FWBDataExtracService = require('../services/FWBDataExtracService')
router.get('/GetDataFromFWB', async (req, res, next) => {
    try {
        .... ....
        // ### THIS WILL FAIL AND AN ERROR WILL BE THROWN
        const FWBJson = await FWBDataExtracService.getFWBData();
        .... ....
    } catch(err) {
        // ### ERR IS ALWAYS EMPTY
        console.log("*", JSON.stringify(err));
        return res.send({'Error': JSON.stringify(err)});
    }
})

As the error was mimicked I was expecting the error to be caught and print out the err message. But err was always empty.

Try to show what `err.stack` displays? – snd Jun 09 '21 at 00:08 — snd, Jun 09 '21 at 00:08

score 4 · Accepted Answer · answered Jun 09 '21 at 00:01

The precise location of error properties is not specified. In some environments, it's on the error object itself - in some, it's on the prototype, or is a getter, or something like that.

JSON.stringify will only iterate over enumerable own properties. In Chrome, the .message property is not enumerable, so it won't be included when stringified:

const e = new Error('foo');
console.log(Object.getOwnPropertyDescriptor(e, 'message'));

Best approach here would be to explicitly extract the properties you want instead of using JSON.stringify. Change

console.log("*", JSON.stringify(err));

to something like

const { message } = err;
console.log("*", message);
 return res.send({ Error: message });

Async - Await JavaScript: unable to catch error details from an Error object

1 Answers1