Cannot

A broken promise resolver.

Aiding in creating consistently human readable messages without compromising machine processing ability. Cannot extends the base Error, can be thrown and behaves just like expected. With a sweet syntax.

Install

$ npm install cannot

Core
An error can be expressed by calling cannot(verb, object) as a function which will return a Broken instance. A Broken instance can also be thrown like a generic Error.

throw cannot('attend', 'the party').because('I fell into a rabbit hole');  
// err.message   -> {String} "I could not attend the party, because I fell into a rabbit hole."  
// err.code      -> {String} "cannot_attend_the_party"  
// err.reason    -> {String} "i_fell_into_a_rabbit_hole"

Semantics

Cannot follows a very simple syntax. It helps you to reason about what really went wrong by avoiding inconsistent error codes, to allow the implementation of recovery strategies.

// Tell me what the problem is...
throw I.cannot('do', 'my work')
  .because(TheDatabase.cannot('find', 'what I was looking for')
    .because('something is broken'));

Subject cannot perform verb/action on object/data, because it had a reason.

The generated message aims to be as user friendly as possible, without spoiling risky information. All error specific data which you need to handle it elsewhere in your application, is derived from your simple declaration.
The because api helps you to specify a reason, which allows you to stack error instances like a Broken as well.

Stacking Errors

Broken instances can be stacked onto each other by handing them over as a reason to the next error.

var err1 = Cannot('do', 'what I should do');
var err2 = Cannot('do', 'what I should do').because(err1);
var err3 = Cannot('do', 'what I should do').because(err2);

console.log(err3.message);

This should produce the following output:

I could not do what I should do
    because I could not do what I should do
    because I could not do what I should do. (No reason)

For more information on stacking errors, have a look at the examples

Reasons

Throwing errors without a reason doesn't make sense, does it? So the majority of errors have a reason which is known, like "because the database had a hiccup" or "the network was down". Cannot errors support reasons to make handling them easier than reacting to a single error code of "user_loading_failed" or "connection_failure".

Recovery

Brokens should be handled and never ever be silently dropped. Most errors can be recovered from, which makes the overall user experience better and the application more stable as it becomes self sufficient. This approach supports a Self Healing Architecture, in which the application can reason about what happened and choose a recovery strategy accordingly.

Contribute

Develop

To start developing, check out this repository and do:

$ make dev

Installs the initial dev dependencies, sets up git hooks and checks linting to be able run mincov before you push. Happy hacking!

Make

For all make targets see:

$ make help

Tests

We are handling errors, not producing them. That said, it is unavoidable to run into issues, but a 100% test coverage helps making sure the demons don't return. Mocha is the test runner in use, extended by expect.js and should within a BDD setup.

$ make test

Specs

To add a feature to development, write a test to add to the spec in a feature branch.

$ make specs

Creates the specs file. cat specs.

Coverage

To generate a test coverage report, it uses istanbul.

$ make coverage

License

(The MIT License)

Copyright (c) 2017 Sebastian Herrlinger (https://github.com/kommander)

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the 'Software'), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED 'AS IS', WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.