# Cancellable Promises

The concept of this kind of cancellable promises was developed for internal usage to make certain things work. The only difference between a native promise and cancellable promise from a client code view is a `.cancel` method which can be used to reject a promise from the outside world. It still can be passed to native promise methods like `Promise.all, Promise.race`, etc.

## Example usage

```javascript
import { createCancellablePromise } from 'csp-coffee/cancellablePromise'

const { cancellablePromise, resolve, reject } = createCancellablePromise(() => {
    console.log('Do something when promise is cancelled');
})
```

`createCancellablePromise` function accepts an `onCancel` callback which is called when promise is cancelled. It returns an object with our `cancellablePromise` and two methods: `resolve` and `reject`. `resolve` and `reject` act exactly like a `resolve` and `reject` inside a promise constructor and provide a way to control a promise from the outside.  Value inside of a `cancellablePromise` property contains our promise with a `.cancel` method.

## Cancelling the promise

### cancel: (reason?: any) => Promise\<void>

`.cancel` accepts any value as an argument and this is a value the `onCancel` callback will be called with. It returns a promise which resolves once cancellation is done

```javascript
import { createCancellablePromise } from 'csp-coffee/cancellablePromise'

const { cancellablePromise, resolve, reject } = createCancellablePromise((message: string) => {
    console.log(message);
});

cancellablePromise.cancel('I AM CANCELLED')

// Will log 'I AM CANCELLED' to the console
```