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Introduction

When you need to listen to a hotkey, you would normally use the onKeyDown event listener. In twenty-front however, you might have conflicts between same hotkeys that are used in different components, mounted at the same time. For example, if you have a page that listens for the Enter key, and a modal that listens for the Enter key, with a Select component inside that modal that listens for the Enter key, you might have a conflict when all are mounted at the same time.

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The useScopedHotkeys hook

To handle this problem, we have a custom hook that makes it possible to listen to hotkeys without any conflict. You place it in a component, and it will listen to the hotkeys only when the component is mounted AND when the specified hotkey scope is active.

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How to listen for hotkeys in practice?

There are two steps involved in setting up hotkey listening :
  1. Set the hotkey scope that will listen to hotkeys
  2. Use the useScopedHotkeys hook to listen to hotkeys
Setting up hotkey scopes is required even in simple pages, because other UI elements like left menu or command menu might also listen to hotkeys.

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Use cases for hotkeys

In general, you’ll have two use cases that require hotkeys :
  1. In a page or a component mounted in a page
  2. In a modal-type component that takes the focus due to a user action
The second use case can happen recursively : a dropdown in a modal for example.

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Listening to hotkeys in a page

Example : 
const PageListeningEnter = () => {
  const {
    setHotkeyScopeAndMemorizePreviousScope,
    goBackToPreviousHotkeyScope,
  } = usePreviousHotkeyScope();

  // 1. Set the hotkey scope in a useEffect
  useEffect(() => {
    setHotkeyScopeAndMemorizePreviousScope(
      ExampleHotkeyScopes.ExampleEnterPage,
    );

    // Revert to the previous hotkey scope when the component is unmounted
    return () => {
      goBackToPreviousHotkeyScope();
    };
  }, [goBackToPreviousHotkeyScope, setHotkeyScopeAndMemorizePreviousScope]);

  // 2. Use the useScopedHotkeys hook
  useScopedHotkeys(
    Key.Enter,
    () => {
      // Some logic executed on this page when the user presses Enter
      // ...
    },
    ExampleHotkeyScopes.ExampleEnterPage,
  );

  return <div>My page that listens for Enter</div>;
};

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Listening to hotkeys in a modal-type component

For this example we’ll use a modal component that listens for the Escape key to tell its parent to close it. Here the user interaction is changing the scope. 
const ExamplePageWithModal = () => {
  const [showModal, setShowModal] = useState(false);

  const {
    setHotkeyScopeAndMemorizePreviousScope,
    goBackToPreviousHotkeyScope,
  } = usePreviousHotkeyScope();

  const handleOpenModalClick = () => {
    // 1. Set the hotkey scope when user opens the modal
    setShowModal(true);
    setHotkeyScopeAndMemorizePreviousScope(
      ExampleHotkeyScopes.ExampleModal,
    );
  };

  const handleModalClose = () => {
    // 1. Revert to the previous hotkey scope when the modal is closed
    setShowModal(false);
    goBackToPreviousHotkeyScope();
  };

  return <div>
    <h1>My page with a modal</h1>
    <button onClick={handleOpenModalClick}>Open modal</button>
    {showModal && <MyModalComponent onClose={handleModalClose} />}
  </div>;
};
Then in the modal component : 
const MyDropdownComponent = ({ onClose }: { onClose: () => void }) => {
  // 2. Use the useScopedHotkeys hook to listen for Escape.
  // Note that escape is a common hotkey that could be used by many other components
  // So it's important to use a hotkey scope to avoid conflicts
  useScopedHotkeys(
    Key.Escape,
    () => {
      onClose()
    },
    ExampleHotkeyScopes.ExampleModal,
  );

  return <div>My modal component</div>;
};
It’s important to use this pattern when you’re not sure that just using a useEffect with mount/unmount will be enough to avoid conflicts. Those conflicts can be hard to debug, and it might happen more often than not with useEffects.

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What is a hotkey scope?

A hotkey scope is a string that represents a context in which the hotkeys are active. It is generally encoded as an enum. When you change the hotkey scope, the hotkeys that are listening to this scope will be enabled and the hotkeys that are listening to other scopes will be disabled. You can set only one scope at a time. As an example, the hotkey scopes for each page are defined in the PageHotkeyScope enum: 
export enum PageHotkeyScope {
  Settings = 'settings',
  CreateWorkspace = 'create-workspace',
  SignInUp = 'sign-in-up',
  CreateProfile = 'create-profile',
  PlanRequired = 'plan-required',
  ShowPage = 'show-page',
  PersonShowPage = 'person-show-page',
  CompanyShowPage = 'company-show-page',
  CompaniesPage = 'companies-page',
  PeoplePage = 'people-page',
  OpportunitiesPage = 'opportunities-page',
  ProfilePage = 'profile-page',
  WorkspaceMemberPage = 'workspace-member-page',
  TaskPage = 'task-page',
}
Internally, the currently selected scope is stored in a Recoil state that is shared across the application : 
export const currentHotkeyScopeState = createState<HotkeyScope>({
  key: 'currentHotkeyScopeState',
  defaultValue: INITIAL_HOTKEYS_SCOPE,
});
But this Recoil state should never be handled manually ! We’ll see how to use it in the next section.

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How is it working internally?

We made a thin wrapper on top of react-hotkeys-hook that makes it more performant and avoids unnecessary re-renders. We also create a Recoil state to handle the hotkey scope state and make it available everywhere in the application.