Cancelable snippet

cancelable.js

/* @flow */
'use strict';

/**
 * A Cancelable is a proxy for a function which supports cancelation.
 * When a cancelable is called, it will pass its arguments to the underlying
 * function, unless it is canceled in which case it will become a no-op.
 *
 * We need this as there's now way atm to cancel promise already running,
 * so what were're doing here is changing the execution callback to empty
 * callback.
 *
 * eg.
 *   c = cancelable(arg => doSomethingWithArg(arg));
 *   c.cancel(); // "cancel" the promise so that doSomethingWithArg
 *               // is never called.
 */

export default function cancelable(fn: Function) : Function {
  let _fn = fn;
  let cancelableFn:Function = (...args: any[]) => _fn(...args);
  let cancelableInterface:Function = (...args) => cancelableFn(...args);
  cancelableInterface.cancel = () => {
    _fn = () => { };
  };
  return cancelableInterface;
}