schwarzkopfb / cer

create fast and correct error constructors

cer

Utility to generate fast and correct custom error constructors. This module exposes a factory function that creates error constructors which are identical to the built-in Error function.

Basic usage

const error   = require('cer'),
      MyError = error('MyError'),
      err     = new MyError('example')

The following comparisons will always resolve to true:

MyError.name === 'MyError'
err.name === 'MyError'
err.message === 'example'
err instanceof Error
err instanceof MyError

Stack trace is similar to the following:

MyError: example
    at Object.<anonymous> (example.js:3:16)
    at Module._compile (module.js:570:32)
    at Object.Module._extensions..js (module.js:579:10)
    at Module.load (module.js:487:32)
    at tryModuleLoad (module.js:446:12)
    at Function.Module._load (module.js:438:3)
    at Module.runMain (module.js:604:10)
    at run (bootstrap_node.js:394:7)
    at startup (bootstrap_node.js:149:9)
    at bootstrap_node.js:509:3

As you can see, irrelevant stack frames after error instantiation aren't appear in trace.

Custom constructor

You can provide a custom constructor to do your own initialization when a new instance is being created.

const error   = require('cer'),
      MyError = error('MyError', init),
      err     = new MyError('foo', 'bar')

function init(message, errorCode) {
    this.code = errorCode
}

And then:

err.message === 'foo' // assigned automatically
err.code === 'bar'

Multiple inheritance

const error = require('cer'),
      DatabaseError = error('DatabaseError'),
      EntityDoesNotExistError = error('EntityDoesNotExistError', init, DatabaseError),
      err = new EntityDoesNotExistError('invalid id provided', 1)

function init(message, id) {
    this.id = id
}

And then:

err instanceof Error
err instanceof DatabaseError
err instanceof EntityDoesNotExistError
err.id === 1

Note: init is not required when you just want to inherit, you can pass a null instead.

Extending prototype

const error   = require('cer'),
      MyError = error('MyError')

MyError.prototype.example = 42

const err = new MyError

And then:

err.example === 42

Note: it works even if you do multiple inheritance.

Installation

With npm:

npm install cer

Tests & benchmarks

Run the unit test suite:

npm test

Run unit tests and create coverage report:

npm run cover

Run benchmarks:

npm run bench

License

MIT