res.json(err) causes "Converting circular structure to JSON" about longjohn HOT 7 CLOSED

You can use https://npmjs.org/package/json-stringify-safe to stringify the error and pass that into res.json.

from longjohn.

Mmmmhhh, thanks for that. Why is Express not using it then?

from longjohn.

It would add some overhead to every single response that uses res.json, which express can't assume a user would be willing to take on. It just doesn't make sense for the framework to make those types of choices for users.

from longjohn.

Makes sense, thx

from longjohn.

I found a better way without adding much overhead nor an external module. I modified the toJSON method like that:

Object.defineProperty(Error.prototype, 'toJSON', {
    value: function() {
        var json = {};

        Object.getOwnPropertyNames(this).forEach(function(key) {
            // ignore long john stuff like '__cached_trace__'
            if (!/__(.)+__/.test(key)) {
                json[key] = this[key];
            }
        }, this);

        return json;
    },
    configurable: true
});

from longjohn.

This definitely works. Be careful when augmenting the core prototypes. You're better off usually adding a method, like toCleanJSON or something like that so that the core type still operates as expected by any other code that may utilize it.

from longjohn.

@mattinsler Agree with you. I just changed that into toCleanJSON in my code.

from longjohn.