watchable-promise

A Promise whose state and value you can read

Installation

npm install watchable-promise

Usage

• Directly create a WatchablePromise instance:

  import WatchablePromise from "watchable-promise";
  
  const p = new WatchablePromise(resolve => setTimeout(() => resolve("foo"), 100));
  
  console.log(p.state); // pending
  console.log(p.settled); // false
  console.log(p.value); // undefined
  
  const val = await p;
  
  console.log(val) // "foo"
  console.log(p.state); // fulfilled
  console.log(p.settled); // true
  console.log(p.value); // "foo"

• Using an existing Promise instance:

  import WatchablePromise from 'watchable-promise';
  
  const existingPromise = new Promise(resolve => setTimeout(() => resolve("foo"), 100));
  const p = WatchablePromise.from(existingPromise);
  
  console.log(p.state); // pending
  console.log(p.settled); // false
  console.log(p.value); // undefined
  
  const val = await p;
  
  console.log(val) // "foo"
  console.log(p.state); // fulfilled
  console.log(p.settled); // true
  console.log(p.value); // "foo"

• Using WatchablePromise.withResolvers():

  import WatchablePromise from 'watchable-promise';
  
  const { promise, resolve, reject } = WatchablePromise.withResolvers();
  
  console.log(promise.state); // pending
  console.log(promise.settled); // false
  console.log(promise.value); // undefined
  
  await resolve("foo");
  
  console.log(promise.state); // fulfilled
  console.log(promise.settled); // true
  console.log(promise.value); // "foo"

• You can call .resolve() or .reject() on a WatchablePromise instance to resolve or reject it externally:

  import WatchablePromise from "watchable-promise";
  
  // Resolving
  const p1 = new WatchablePromise(resolve => {});
  p1.resolve("foo");
  const val = await p1;
  console.log(val) // "foo"
  
  // Rejecting
  const p2 = new WatchablePromise((resolve, reject) => {});
  p2.reject("bar");
  try {
      await p2;
  } catch (err) {
      console.log(err) // "bar"
  }

License

watchable-promise is released under the Apache 2.0 License. See the enclosed LICENSE for details.

Disclaimer

This is not an officially supported Google product. I just happen to work there.