ES20xx cancellable function proposal

cancellable.js

cancellable function foo() { // extends `async function` and introduces `queue` keyword
  let b = queue bar(); // can be auto canceled by cancelling foo
  b === cancellation // true when foo is canceled during bar call, otherwise false
  await bac(); // will not be auto canceled
}

let baz = foo();
baz.cancel();
baz === cancellation // true, new `cancellation` variable for function cancellation

let { baw, bax } = await baz;
baw === cancellation // true, cancellation.any is also cancellation

let bay = (await baz)();
bay === cancellation // true, cancellation() is cancellation

promise.d.ts

// Promise spec should be extended

interface PromiseController {
  canceled: boolean;
  confirmCancellation: () => Promise<void>;
}

interface PromiseOptionBag {
  revert?: (status: string) => any | PromiseLike<any>;
  precancel?: () => any | PromiseLike<any>;
  deferCancellation?: boolean;
}

extended class Promise<T> {
  constructor(
    init: (
      resolve: (value?: T | PromiseLike<T>) => Promise<void>,
      reject: (reason?: any) => void | PromiseLike<void>,
      controller: PromiseController
    ) => any,
    options: PromiseOptionBag
  ): Promise<T>;
  
  [Symbol.cancel](): Promise<void>;
  
  cancel(): Promise<void>;
}