do not overwrite the error stack in json parser

[bjohansebas]

This is just a reminder that we need to stop overwriting the stack, and use error.cause or something similar.

Discovered in #604

[wesleytodd]

error.cause! Also, often in cases like this the stack can be pretty unhelpful to end users, so you can use Error.captureStackTrace in some cases to help make more clear traces back into user code.

[mahmoodhamdi]

I'd be interested in helping with this. Looking at the json parser, the stack overwrite happens because the error is created first, then later re-thrown with a different message — losing the original stack trace context.

Using error.cause (ES2022, Node.js 16.9+) would preserve the full chain:

// Instead of overwriting the stack:
var err = createError(400, 'entity parse failed')
err.cause = originalError  // preserves original error + its stack

This way err.stack points to where body-parser detected the problem, and err.cause.stack points to where the underlying parse actually failed — much more useful for debugging.

Since body-parser currently supports Node.js >= 0.8, would this be gated behind the v2 major release, or could it be done with a feature check for environments that support cause?

[Phillip9587]

@mahmoodhamdi There already is a PR #622 but we have to wait for the next major relase to remove this behavior.