Cancellable (this package in development, do not use it)

Wrapper to create cancellable promises.

A Promise cannot be canceled since once it is created and fulfillment or a rejection handler is registered to it, there is no external mechanism to stop its progression. A Cancellable wraps the ES6 standard Promise, and it is compatible with whatever promise-consuming tool.

Status

Installation

npm install --save pcancellable

or

yarn add pcancellable

What is a Cancellable

A Cancellable implements the same methods of a standard ES6 Promise, however:

• It can be canceled. Once the .cancel() method is called it notifies all registered resolution handlers.
• The constructor executor parameter receives an additional onCancel argument is executed once the .cancel() is called.

API

Cancellable

The constructor has a single parameter - the Cancellable resolver, which is a function that is passed with the arguments resolve, reject and onCancel. The onCancel is a function that receives an handler which that is called once the Cancellable is canceled.

const delay = delta => {
  return new Cancellable((resolve, reject, onCancel) => {
    const id = setTimeout(() => {
      resolve(id);
    }, delta);

    // Called when canceled.
    onCancel(() => {
      clearTimeout(id);

      console.log(`Cancelled! ${id}`);
    });
  });
};

// Without cancelation.
delay(100)
  .then(console.log); // > '1'

// With cancelation.
delay(100)
  .then(console.log) // Not called.
  .cancel(); // > 'Cancelled 1'

Static methods

Cancellable.all(iterable: Iterable<T>): Cancellable<Array<T>>

Has the same behaviour as the Promise.all method, except when it is canceled it cancels all Cancellables included on the iterable argument.

Returns a cancellable that either fulfills when all of the values in the iterable argument have fulfilled or rejects as soon as one of the cancellables in the iterable argument rejects. This method wraps the Promise.all method and creates a list of cancellables that are canceled when .cancel() is called.

// Without cancelation.
Cancellable
  .all(['foo', delay(1), delay(2)])
  .then(console.log); // > ['foo', 1, 2]

// With cancelation.
Cancellable
  .all([delay(1), delay(2)])
  .then(console.log); // Not called.
  .cancel()
  // > Cancelled 1
  // > Cancelled 2

Cancellable.race(iterable: Iterable<T>): Cancellable<T>

Has the same behaviour as the Promise.race method, except when it is canceled it cancels all Cancellables included on the iterable argument. Returns a cancellable that fulfills or rejects as soon as one of the cancellables in the iterable fulfills or rejects, with the value or reason from that cancellable. This method wraps the Promise.all method and creates a list of cancellables that are canceled when .cancel() is called.

// Without cancelation.
Cancellable
  .race([delay(1), delay(2)])
  .then(console.log); // > 1

// With cancelation.
Cancellable
  .all([delay(1), delay(2)])
  .then(console.log); // Not called.
  .cancel()
  // > Cancelled 1
  // > Cancelled 2

Cancellable.resolve(value: any)

Has the same behavior as the Promise.resolve method. Returns a Cancellable object that is resolved with the given value. If the value is a thenable (i.e. has a then method), the returned cancellable will unwrap that thenable, adopting its eventual state. Otherwise the returned cancellable will be fulfilled with the value.

Cancellable.reject(value: any)

Has the same behavior as the Promise.reject method. Returns a Cancellable object that is rejected with the given reason.

Cancellable.isCancellable(value: any): boolean

Determines whether the passed value is a Cancellable.

Instance methods

Cancellable.prototype.isCanceled(): boolean

Determines whether the created Cancellable is canceled.

Cancellable.prototype.cancel(callback?: Function)

Cancels the Cancellable. It iterates upwards the chain canceling all the registered cancellables including its children. Unlike other implementations that rejects the promise when it is canceled, the cancel method receives an optional callback that is passed to the onCancel function. This way it is possible to cancel a cancellable without unhandled rejections.

const delay = delta => new Cancellable((resolve, reject, onCancel) => {
  const id = setTimeout(() => {
    resolve();
  });

  onCancel(cb => {
    clearTimeout(id);
    cb(id);
  });
});

delta(1000).cancel(() => {
  console.log(`Timeout "${id}" was canceled!`)
}); // > Timeout "1" was canceled!

Cancellable.prototype.catch(onRejected: Function): Cancellable

Has the same behavior of Promise.catch method. Appends a rejection handler callback to the cancellable, and returns a new Cancellable resolving to the return value of the callback if it is called, or to its original fulfillment value if the cancellable is instead fulfilled.

Cancellable.prototype.then(onFullfilled: Function, onRejected: Function): Cancellable

Has the same behavior of Promise.then method. Appends fulfillment and rejection handlers to the cancellable, and returns a new Cancellable resolving to the return value of the called handler, or to its original settled value if the promise was not handled.

Licence

MIT © João Granado