@abraham/remotedata

RemoteData

Lightweight TypeScript RemoteData implementation

Install

npm install @abraham/remotedata

Usage

Read Slaying a UI Antipattern with Web Components (and TypeScript) for a more thorough guide.

This is an example class that gets a tweet (type Status) from a remote HTTP API.

import { Failure, fold, Initialized, Pending, RemoteData, Success } from '@abraham/remotedata';
import { Status } from 'twitter-d';

// Define what the RemoteData Failure and Success types will be.
type State = RemoteData<number, Status>;

class Thing {
  // Set the initial state as Initialized.
  private state: State = new Initialized();

  constructor() {
    // On instantiation start the remote call and render the current state.
    this.getStatus();
    this.render();
  }

  private async function getStatus() {
    // Before starting the remote call set the current state to Pending.
    this.state = new Pending();
    // Perform the actual remote request.
    const response = await fetch('https://api.example.com/tweet');
    if (response.ok) {
      // If the request succeeds set the state to Success with the returned data.
      const status: Status = await response.json();
      this.state = new Success(status);
    } else {
      // If the request does not succeed set the state to Failure with the reason.
      this.state = new Failure(status_code);
    }
    // Render the new state.
    this.render();
  }

  private get view(state: State): (state: State) => string {
    // Use `fold` to easily define logic based on the current state.
    // Fold takes four methods as parameters in the order of Initialized, Pending, Failure, and
    // Success and returns a method that takes a `RemoteData` state instance as a parameter. When
    // the returned method gets called with a `RemoteData` state, the method matching the correct
    // state gets called.
    return fold<string, number, Status>(
      // What to do if the state is Initialized.
      () => 'Initialized',
      // What to do if the request is Pending.
      () => 'Loading...',
      // What to do if the request fails.
      (error: number) => `Error: ${error}`,
      // What to do if the request succeeds.
      (status: Status) => `Got tweet from ${status.screen_name}`,
    );
  }

  private render(): string {
    // Render the current state in your UI.
    // `this.view` returns a method which is executed with the current state as a parameter.
    const text: string = this.view(this.state);
    // Maybe put it in a template.
  }
}

Using included type guards.

import { RemoteData } from '@abraham/remotedata';
import { Status } from 'twitter-d';
import { getState } from './state';

// Define what the RemoteData Failure and Success types will be.
type State = RemoteData<number, Status>;

const state: State = getState();
if (isSuccess(state)) {
  // state is known to be of type Success<Status>
  console.log(state.data.full_text);
}

References

• How Elm Slays a UI Antipattern
• Slaying a UI Antipattern with Angular
• Slaying a UI Antipattern with Flow
• Slaying a UI Antipattern in React
• Slaying a UI Antipattern in Fantasyland
• Remote Data State as an Enum