Deferred

Tiny extension for native Promises to make them more suitable for Node core APIs. The package exposes a subclass of the built-in Promise, which extends that with the following four methods.

new Deferred([executor])

Unlike Promise, Deferred does not require an executor function for instantiation, because it makes possible to resolve or reject the instance from outside the executor's scope.

const d1 = new Deferred,
      d2 = new Deferred(executor)

d1.resolve('sun is shining')
      
function executor(resolve, reject) {
    reject('baby is crying') // same as d2.reject(...)
}

d1.then(result => console.log('success:', result))
d2.catch(error => console.error('error:', error))

Output:

success: sun is shining
error: baby is crying

deferred.resolve(value)

Resolve the deferred instance.

deferred.reject(reason)

Reject the deferred instance.

deferred.done(callback)

Attach an error-first callback to the instance. It will be fired once the instance resolves or rejects.

const d1 = new Deferred,
      d2 = new Deferred
      
function handler(err, result) {
    if (err)
        console.error('error:', err)
    else
        console.log('success:', result)
}

d1.done(handler)
d2.done(handler)

d1.resolve('your pizza order has arrived')
d2.reject('something exploded')

Output:

success: your pizza order has arrived
error: something exploded

deferred.callback()

Generate an error-first callback which will resolve or reject the instance based on the first parameter passed to it.

const d1 = new Deferred,
      d2 = new Deferred,
      cb1 = d1.callback(),
      cb2 = d2.callback()
      
d1.then(result => console.log('success:', result))
d2.catch(error => console.error('error:', error))

cb1(null, 'your cat is purring')
cb2('coffee machine is out of order')

Output:

success: your cat is purring
error: coffee machine is out of order

Installation

With npm:

npm install defd

Tests

Run unit tests:

npm test

Run unit tests and create coverage report:

npm run cover

License

MIT