async-await.js

// Make an API asynchronous
// In this example, we mock an iOS Keychain class. All operations
// are async (I/O), so when we use this mock in our tests, we
// want the operations to act async even though it's not needed
// for the class to work
class KeychainMock {
  store: [],
  async get(key) {
    return this.store[key] || null;
  }
  async set(key, value, useTouchId) {
    this.store[key] = { value, useTouchId };
  }
  async remove(key) {
    delete this.store[key];
  }
}

promises.js

/* Promises implementation */
// `async` wraps functions in promises very neatly.
class KeychainMock {
  store: [],
  get(key) {
    return Promise.resolve(this.store[key] || null);
  }
  set(key, value, useTouchId) {
    this.store[key] = { value, useTouchId };
    return Promise.resolve();
  }
  async remove(key) {
    delete this.store[key];
    
    return Promise.resolve();
  }
}