fromPromise which starts with fulfilled state

We mostly use fromPromise to render loading or other states in react components. Here is a sample component:

@observer
class MyComponent extends React.Component {
  @action componentDidMount() {
    this.entity = this.props.store.getEntity();  // getEntity returns a `IPromiseBasedObservable`
  }

  @observable entity = fromPromise(Promise.resolve());

  render() {
    return this.entity.case({
      fulfilled: value => (<div>{JSON.stringify(value)}</div>),
      rejected: error => (<div>Error</div>),
      pending: () => (<div>Loading entity...</div>)
    });
  }
}

I have initialized entity with a resolved fromPromise to avoid writing an if in render method. What I think is really useful is fromPromise(value). So fromPromise does not necessarily needs a Thenable object.

[jamiewinder]

Just to add, in some circumstances it can be handy to create a PromiseBasedObservable in a static pending or rejected state too. For example:

@computed get data(): IPromiseBasedObservable<Data> {
    const serverData = this.serverData;
    if (serverData.state != REJECTED) {
        return fromPromise.state(serverData.state); // *
    }
    // process local data + server data
}

@computed get serverData(): IPromiseBasedObservable<Data>{
    return fromPromise(fetchServerData);
}

[mweststrate]

3.0.0 introduced the methods fromPromise.reject(value) and fromPromise.resolve(value).