named-functions-in-promises.md

named-functions-in-promises

Use named functions defined on objects to handle promises.

When you use promises and its handlers, use named functions defined on parent object. Thus, you will be able to test them in isolation using unit tests without any additional mocking.

Examples

export default Component.extend({
  actions: {
    // BAD
    updateUserBad(user) {
      user
        .save()
        .then(() => {
          return user.reload();
        })
        .then(() => {
          this.notifyAboutSuccess();
        })
        .catch(() => {
          this.notifyAboutFailure();
        });
    },
    // GOOD
    updateUserGood1(user) {
      user
        .save()
        .then(this._reloadUser.bind(this))
        .then(this._notifyAboutSuccess.bind(this))
        .catch(this._notifyAboutFailure.bind(this));
    },
    // GOOD if allowSimpleArrowFunction: true
    updateUserGood2(user) {
      user
        .save()
        .then(() => this._reloadUser())
        .then(() => this._notifyAboutSuccess())
        .catch(() => this._notifyAboutFailure());
    }
  },
  _reloadUser(user) {
    return user.reload();
  },
  _notifyAboutSuccess() {
    // ...
  },
  _notifyAboutFailure() {
    // ...
  }
});

And then you can make simple unit tests for handlers:

test('it reloads user in promise handler', function (assert) {
  const component = this.subject();
  // assuming that you have `user` defined with kind of sinon spy on its reload method
  component._reloadUser(user);
  assert.ok(userReloadSpy.calledOnce, 'user#reload should be called once');
});

Configuration

This rule takes an optional object containing:

• boolean -- allowSimpleArrowFunction -- (default false) setting to true allows arrow function expressions that do not have block bodies. These simple arrow functions must also only contain a single function call. For example: .then(user => this._reloadUser(user)).