How does GCP Error reporting differentiates errors?

Question

I am trying @google-cloud/error-reporting npm package. I would like to know how Error reporting differentate errors. I often see two different errors being grouped as one error even if they have a different error message and appear at a differente line of code.

Do you have any hints on this?

Here is the simplified code I use for express error handler middleware in App engine standard:

import {ErrorReporting} from '@google-cloud/error-reporting';
const GCPerrorReporting = new ErrorReporting();

export default function(error, req, res, next) {
    GCPerrorReporting.report(error); //The error has a message property
}

Thank you!