Implement promises alongside callbacks

[vernak2539]

• promise integration (non-breaking)
• added tests for all helper functions
• renamed check401header to isValid401 (internal change, not breaking)
• added fallback if respond is given invalid delivery type
• clean up tests a little
• removed all errorPropagatedFrom (people can figure it out)

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fixes #46

[vernak2539]

@dougwilson mind taking a look when you have a sec? want to make sure i didn't mess anything up, or if there's a better way to do something

[dougwilson]

My only initial comment is that it's weird that, when provided a callback, you still get a promise returned.

[vernak2539]

Yeah thought that too, but it was the best way i thought to do it without it being overly complicated. doesn't seem to be too much overhead creating a promise even when using callbacks

[dougwilson]

Gotcha. It's up to you, I was just sharing my opinion :) My concern wasn't performance-related, only what would happen when users did the following

RestClient
    .get(options, function (err, response) {
      // who gets called first, callback or promise?
    })
    .then(function(response) {
        // will be delivered with 200, 400, 401, 500, etc status codes
        // response.body === payload from response
        // response.res === full response from request client
        console.log(response);
    })
    .catch(function(err) {
        // error here
        console.log(err);
    });
}); 

[dougwilson]

FWIW, I have been testing the waters myself on this kind of dual-API at https://github.com/stream-utils/raw-body and https://github.com/crypto-utils/uid-safe

[vernak2539]

Oh I see what you're saying. I think it should be one or the other and people should implement it that way. I can add that to the readme.

Your stuff looks good at a glance, and probably implement something like that in v1.1 or something along those lines.

Appreciate the comments, as always