support "err instanceof http-errors" for all individual errors

[krmannix]

Allows for a broader instanceof check. Rather than needing to check if an error is a specific status code type, one can check for a generic HttpError as well.

var HttpError = require('http-errors');
var notFoundError = HttpError(404);

if (notFoundError instanceof HttpError) {
    // true
}

if (notFoundError instanceof HttpError['404']) {
    // true
}

if (notFoundError.name === 'NotFoundError') {
    // true
}

[krmannix]

As mentioned in #21, builds fail for Node.js 0.6 and 0.8 because of dependencies, not due to the PR

[krmannix]

tests now pass for this pr, and rebased with the most current master branch

[dougwilson]

Thanks a lot! I'm currently mulling over this right now. I am 100% for adding another object into the prototype such that they all inherit from it, i.e. StatusError -> HttpError -> Error. The only thing I'm debating with myself right now is if the actual factory function should be that HttpError class or not, particularly because it will have different semantics than using the other current constructors.

Then, after that, I'm thinking, if the HttpError class is not the factory function, then what should new HttpError() (or new HttpError(message)) actually result in? Should it's signature be new HttpError(code, message)? Perhaps we should say that HttpError is more like an abstract class, and thus just not allow new HttpError(...) at all.

My current thoughts are leaning towards the following:

1. Add a new export, HttpError that all error classes here inherit from. This would thus look like require('http-errors').HttpError.
2. Throw a TypeError when trying to construct that directly, to make it behave like an abstract class.

What are your thoughts? If this sounds good or any other thoughts, let me know. I can easily alter your own pull request to reflect this if you are not around to change it, or just don't fell like it because this sounds like a good enough change.

[krmannix]

My thought would be that the HttpError (or whatever the overall parent object is) eventually should be the factory function, but I think the best change would be what you suggested - it's the least disruptive and fits with the current style of using this module while still allowing for the functionality suggested in this PR.

Please feel free to change it, and thanks!

[dougwilson]

Nice! And, so here's something that may interest you: so, because this module is depending on too large of a version range of statuses, and uses that module to define it's interface, I plan to release a new version version of this module to fix that situation. This means that now is a good time to bring up PRs/discussions around breaking changes :)!

[krmannix]

👍 awesome! I'd be happy to put some thought in and see if I can help out. where will you be listing your proposed changes?

[dougwilson]

where will you be listing your proposed changes?

Feel free to make any issues/PRs you like :) When I get rolling, it'll be in a release PR, like what I've done with Express and other modules (example: expressjs/body-parser#66). This would track the merged things and provide an overview of the progress and goals at the top.