lrud

A React library for managing focus in LRUD applications.

Motivation

The native focus system that ships with browsers is one-dimensional: users may only move forward and back. Some applications (typically those that use remote controls or video game controllers) require a two dimensional focus system.

Because of this, it is up to the application to manage its own focus state. That's where this library comes in: it makes working with two dimensional focus seamless.

Installation

Install using npm:

npm install @please/lrud

or yarn:

yarn add @please/lrud

This library has the following peer dependencies:

react@^16.8.0 || react@^17.0.0

Guides
API Reference
Interfaces
Examples
Prior Art

Guides

Basic Setup

Render the FocusRoot high up in your application's component tree.

import { FocusRoot } from '@please/lrud';

export default function App() {
  return (
    <FocusRoot>
      <AppContents />
    </FocusRoot>
  );
}

You may then use FocusNode components to create a focusable elements on the page.

import { FocusNode } from '@please/lrud';

export default function Profile() {
  return <FocusNode className="profile">Profile</FocusNode>;
}

This library automatically moves the focus between the FocusNodes as the user inputs LRUD commands on their keyboard or remote control.

This behavior can be configured through the props of the FocusNode component. To learn more about those props, refer to the API documentation below.

Getting Started

The recommended way to familiarize yourself with this library is to begin by looking at the examples. The examples do a great job at demonstrating the kinds of interfaces you can create with this library using little code.

Once you've checked out a few examples you should be in a better position to read through these API docs!

FAQ

What is LRUD?

LRUD is an acronym that stands for left-right-up-down, and it refers to the directional buttons typically found on remotes. In LRUD systems, input devices usually also have some kind of "submit" button, and, less commonly, a back button.

API Reference

This section of the documentation describes the library's named exports.

`<FocusRoot />`

Serves as the root node of a new focus hierarchy. There should only ever be one FocusRoot in each application.

All props are optional.

Prop	Type	Default value	Description
`orientation`	string	`'horizontal'`	Whether the children of the root node are arranged horizontally or vertically.
`wrapping`	boolean	`false`	Set to `true` for the navigation to wrap when the user reaches the start or end of the root's children.
`pointerEvents`	boolean	`false`	Set to `true` to enable pointer events. Read the guide.

import { FocusRoot } from '@please/lrud';

export default function App() {
  return (
    <FocusRoot orientation="vertical">
      <AppContents />
    </FocusRoot>
  );
}

`<FocusNode />`

A Component that represents a focusable node in your application.

All props are optional. Example usage appears beneath the props table.

Prop	Type	Default value	Description
`propsFromNode`	function		A function you can supply to compute additional props to apply to the element. The function is passed one argument, the focus node.
`className`	string		A class name to apply to this element.
`focusedClass`	string	"isFocused"	A class name that is applied when this element is focused.
`focusedLeafClass`	string	"isFocusedLeaf"	A class name that is applied this element is a focused leaf.
`activeClass`	string	"isActive"	A class name that is applied this element is active.
`disabledClass`	string	"focusDisabled"	A class name that is applied this element is disabled.
`elementType`	string\|elementType	'div'	The React element type to render. For instance, `"img"` or `motion.div`.
`focusId`	string	`{unique_id}`	A unique identifier for this node. Specify this yourself for debugging purposes, or when you will need to manually set focus to the node.
`orientation`	string	'horizontal'	Whether the children of this node are arranged horizontally or vertically. Pass `"vertical"` for vertical lists.
`wrapping`	boolean	`false`	Set to `true` for the navigation to wrap when the user reaches the start or end of the children list. For grids this sets wrapping in both directions.
`wrapGridHorizontal`	boolean	`false`	Set to `true` for horizontal navigation in grids to wrap.
`wrapGridVertical`	boolean	`false`	Set to `true` for vertical navigation in grids to wrap.
`disabled`	boolean	`false`	This node will not receive focus when `true`.
`isGrid`	boolean	`false`	Pass `true` to make this a grid.
`isTrap`	boolean	`false`	Pass `true` to make this a focus trap.
`forgetTrapFocusHierarchy`	boolean	`false`	Pass `true` and, if this node is a trap, it will not restore their previous focus hierarchy when becoming focused again.
`onMountAssignFocusTo`	string		A focus ID of a nested child to default focus to when this node mounts.
`defaultFocusChild`	number\|function		The child index that should receive focus when focus is assigned to this focus node. Does not work with grids. We strongly recommend using `useCallback` when using the function form to avoid infinite render loops.
`defaultFocusColumn`	number	`0`	The column index that should receive focus when focus is assigned to this focus node. Applies to grids only.
`defaultFocusRow`	number	`0`	The row index that should receive focus when focus is assigned to this focus node. Applies to grids only.
`isExiting`	boolean		Pass `true` to signal that this node is animating out. Useful for certain kinds of exit transitions.
`onFocused`	function		A function that is called when the node receives focus. Passed one argument, an FocusEvent.
`onBlurred`	function		A function that is called when the node loses focus. Passed one argument, an FocusEvent.
`onKey`	function		A function that is called when the user presses any TV remote key while this element has focus. Passed one argument, an LRUDEvent.
`onArrow`	function		A function that is called when the user presses a directional button. Passed one argument, an LRUDEvent.
`onLeft`	function		A function that is called when the user presses the left button. Passed one argument, an LRUDEvent.
`onUp`	function		A function that is called when the user presses the up button. Passed one argument, an LRUDEvent.
`onDown`	function		A function that is called when the user presses the down button. Passed one argument, an LRUDEvent.
`onRight`	function		A function that is called when the user presses the right button. Passed one argument, an LRUDEvent.
`onSelected`	function		A function that is called when the user pressed the select button. Passed one argument, an LRUDEvent.
`onBack`	function		A function that is called when the user presses the back button. Passed one argument, an LRUDEvent.
`onMove`	function		A function that is called when the focused child index of this node changes. Only called for nodes with children that are not grids. Passed one argument, a MoveEvent.
`onGridMove`	function		A function that is called when the focused child index of this node changes. Only called for grids. Passed one argument, a GridMoveEvent.
`children`	React Node(s)		Children of the Focus Node.
`...rest`	any		All other props are applied to the underlying DOM node.

import { FocusNode } from '@please/lrud';

export default function Profile() {
  return (
    <FocusNode
      elementType="button"
      className="profileBtn"
      onSelected={({ node }) => {
        console.log('The user just selected this profile', node);
      }}>
      Profile
    </FocusNode>
  );
}

`useFocusNodeById( focusId )`

A Hook that returns the focus node with ID focusId. If the node does not exist, then null will be returned instead.

import { useFocusNodeById } from '@please/lrud';

export default function MyComponent() {
  const navFocusNode = useFocusNodeById('nav');

  console.log('Is the nav focused?', navFocusNode?.isFocused);
}

`useLeafFocusedNode()`

A Hook that returns the currently-in-focus leaf node.

import { useLeafFocusedNode } from '@please/lrud';

export default function MyComponent() {
  const currentFocusedNode = useLeafFocusedNode();

  console.log('Currently focused node', currentFocusedNode);
}

`useActiveNode()`

A Hook that returns the active focus node, or null if no node is active. As a reminder, the active node is whatever node was selected last (similar to how interactive elements in the DOM become active after being clicked).

import { useActiveNode } from '@please/lrud';

export default function MyComponent() {
  const activeNode = useActiveNode();

  console.log('The active node:', activeNode);
}

`useSetFocus()`

A Hook that returns the setFocus function, which allows you to imperatively set the focus.

This can be used to:

override the default navigation behavior of the library
focus modals or traps
exit traps

import { useSetFocus } from '@please/lrud';

export default function MyComponent() {
  const setFocus = useSetFocus();

  useEffect(() => {
    setFocus('nav');
  }, []);
}

`useNodeEvents( focusId, events )`

A Hook that allows you to tap into a focus nodes' focus lifecycle events. Use this hook when you need to respond to the focus lifecycle for a node that is not in your current component.

import { useNodeEvents } from '@please/lrud';

export default function MyComponent() {
  useNodeEvents('nav', {
    focus(navNode) {
      console.log('The nav node is focused', navNode);
    }

    blur(navNode) {
      console.log('The nav node is no longer focused', navNode);
    }
  });
}

Each callback receives a single argument, the focus node.

The available event keys are:

Event key	Called when
`focus`	the focus node receives focus.
`blur`	the focus node loses focus.
`active`	the focus node becomes active.
`inactive`	the focus node is no longer active.
`disabled`	the focus node is set as disabled.
`enabled`	the focus node is enabled.

`useFocusHierarchy()`

A Hook that returns an array representing the focus hierarchy, which are the nodes that are currently focused. Each entry in the array is a focus node.

import { useFocusHierarchy } from '@please/lrud';

export default function MyComponent() {
  const focusHierarchy = useFocusHierarchy();

  console.log(focusHierarchy);
  // => [
  //   { focusId: 'root', ... },
  //   { focusId: 'homePage', ... },
  //   { focusId: 'mainNav', ... },
  // ]
}

`useProcessKey()`

A Hook that allows you to imperatively trigger LRUD key presses.

import { useProcessKey } from '@please/lrud';

function MyComponent() {
  const processKey = useProcessKey();

  useEffect(() => {
    // Imperatively trigger a down key press
    processKey.down();

    // Imperatively trigger a back key press
    processKey.select();

    // ...same, for the back button.
    processKey.back();
  }, []);
}

The full API is as follows.

interface ProcessKey {
  select: () => void;
  back: () => void;
  down: () => void;
  left: () => void;
  right: () => void;
  up: () => void;
}

`useFocusStoreDangerously()`

⚠️ Heads up! The FocusStore is an internal API. We strongly discourage you from accessing properties or calling methods on the FocusStore directly!

A Hook that returns the FocusStore. Typically, you should not need to use this hook.

One use-case for this hook is attaching the focusStore to the window when developing, which can be useful for debugging purposes.

import { useFocusStoreDangerously } from '@please/lrud';

export default function MyComponent() {
  const focusStore = useFocusStoreDangerously();

  useEffect(() => {
    if (process.env.NODE_ENV !== 'production') {
      window.focusStore = focusStore;
    }
  }, []);
}

Interfaces

These are the objects you will encounter when using this library.

`FocusNode`

A focus node. Each <FocusNode/> React component creates one of these.

Property	Type	Description
`elRef`	ref	A ref containing the HTML element for this node.
`focusId`	string	A unique identifier for this node.
`children`	Array<string>	An array of focus IDs representing the children of this node.
`focusedChildIndex`	number\|null	The index of the focused child of this node, if there is one.
`prevFocusedChildIndex`	number\|null	The index of the previously-focused child of this node, if there was one.
`isFocused`	boolean	`true` when this node is focused.
`isFocusedLeaf`	boolean	Whether or not this node is the leaf of the focus hierarchy.
`active`	boolean	`true` this node is active.
`disabled`	boolean	`true` when this node is disabled.
`isExiting`	boolean	Set to `true` to indicate that the node will be animating out. Useful for certain exit animations.
`wrapping`	boolean	`true` when the navigation at the end of the node will wrap around to the other side.
`wrapGridVertical`	boolean	`true` when grid rows will wrap.
`wrapGridHorizontal`	boolean	`true` when grid columns will wrap.
`isRoot`	boolean	`true` this is the root node.
`trap`	boolean	`true` when this node is a focus trap.
`forgetTrapFocusHierarchy`	boolean	Set to `false` and a focus trap will restore its previous hierarchy upon becoming re-focused.
`parentId`	string \| `null`	The focus ID of the parent node. `null` for the root node.
`orientation`	string	A string representing the orientation of the node (either `"horizontal"` or `"vertical"`)
`navigationStyle`	string	One of `'first-child'` or `'grid'`
`nodeNavigationItem`	string	How this node is used in the navigation algorithm. Possible values are 'default'`, 'grid-container'`, `'grid-row'`, `'grid-item'`
`defaultFocusColumn`	number	The column index that should receive focus when focus is assigned to this focus node. Applies to grids only.
`defaultFocusRow`	number	The row index that should receive focus when focus is assigned to this focus node. Applies to grids only.
`_gridColumnIndex`	number \| `null`	The focused column index of a grid.
`_gridRowIndex`	number \| `null`	The focused row index of a grid.
`_focusTrapPreviousHierarchy`	Array<string>	The previous focus hierarchy of a trap.

`LRUDEvent`

An object that is passed to you in the LRUD-related callbacks of a FocusNode component:

onKey
onArrow
onLeft
onRight
onUp
onDown
onSelected
onBack

Property	Type	Description
`key`	string	A string representing the key that was pressed. One of `"left"`, `"right"`, `"up"`, `"down"`, `"select"`, or `"back"`.
`isArrow`	boolean	Whether or not this key is an arrow.
`node`	FocusNode	The current `FocusNode` that received this event as the event propagates up the focus hierarchy. Analagous to `event.currentTarget`
`targetNode`	FocusNode	The leaf `FocusNode` from which this event propagated. Analagous to `event.target`
`preventDefault`	function	Call this to stop the default behavior of the event. Commonly used to override the navigation behavior
`stopPropagation`	function	Call this to stop the propagation of the event.

`MoveEvent`

An object that is passed to you in the onMove callback of a FocusNode component.

Property	Type	Description
`orientation`	string	The orientation of the move. Either `"horizontal"` or `"vertical"`.
`direction`	string	The direction of the move. Either `"forward"` or `"back"`.
`arrow`	string	The arrow that was pressed. One of `"up"`, `"down"`, `"left"`, or `"right"`.
`prevChildIndex`	number	The index of the previously-focused child `FocusNode`.
`nextChildIndex`	number	The index of the child `FocusNode` that is now focused.
`prevChildNode`	FocusNode \| `null`	The previously-focused `FocusNode`.
`nextChildNode`	FocusNode	The child `FocusNode` that is now focused.

`GridMoveEvent`

An object that is passed to you in the onGridMove callback of a FocusNode component that is a grid.

Property	Type	Description
`orientation`	string	The orientation of the move. Either `"horizontal"` or `"vertical"`.
`direction`	string	The direction of the move. Either `"forward"` or `"back"`.
`arrow`	string	The arrow that was pressed. One of `"up"`, `"down"`, `"left"`, or `"right"`.
`prevRowIndex`	number	The index of the previously-focused row.
`nextRowIndex`	number	The index of the newly-focused row.
`prevColumnIndex`	number	The index of the previously-focused column.
`nextColumnIndex`	number	The index of the newly-focused column.

`FocusEvent`

An object that is passed to you in the onFocused and onBlurred callbacks of a FocusNode component.

Property	Type	Description
`focusNode`	FocusNode\|`undefined`	The newly-focused leaf `FocusNode`.
`blurNode`	FocusNode\|`undefined`	The previously-focused leaf `FocusNode`.
`currentNode`	FocusNode	The `FocusNode` that is receiving the event, as it traverses the focus hierarchy. Analogous to event.currentTarget.

`FocusStore`

⚠️ Heads up! This is an internal API. We strongly discourage you from accessing properties or calling methods on the FocusStore directly!

An object that represents the store that contains all of the state related to what is in focus. Typically, you should not need to interact with this object directly, but it is made available to you for advanced use cases that you may have.

Property	Type	Description
`getState`	function	Returns the current FocusState
`createNodes`	function	Creates one or more focus nodes in the tree.
`deleteNode`	function	Deletes a focus node from the tree.
`setFocus`	function	Imperatively assign focus to a particular focus node.
`updateNode`	function	Update an existing node. Used to, for example, set a node as disabled.
`processKey`	object	Contains methods to trigger key presses.
`handleArrow`	function	Updates store state after arrow key presses.
`handleSelect`	function	Updates store state after select button presses.
`configurePointerEvents`	function	Enable or disable pointer events. Receives one argument, a `boolean`.
`destroy`	function	Call when disposing of the store. Cleans up event listeners.

`FocusState`

⚠️ Heads up! This is an internal API. We strongly discourage you from accessing this object directly in your application.

An object representing the state of the focus in the app.

Property	Type	Description
`focusedNodeId`	string	The ID of the leaf node in the focus hierarchy.
`focusHierarchy`	Array	An array of node IDs representing the focus hierarchy.
`activeNodeId`	string \| `null`	The ID of the active node, if there is one.
`nodes`	Object	A mapping of all of the focus nodes that exist.
`interactionMode`	string	The active interaction mode of the app. Either `"lrud"` or `"pointer"`.
`_hasPointerEventsEnabled`	boolean	A boolean used internally for managing the creation of nested nodes.
`_hasPointerEventsEnabled`	boolean	Whether or not pointer events are currently enabled.
`_updatingFocusIsLocked`	boolean	A boolean used internally for managing the creation of nested nodes.

Examples

This repository contains example projects showing common patterns when using this library. Each example is located in the ./examples folder.

Instructions for running the examples are found in the README file for each example.

Basic Examples

Basic Layout - Demonstrates using the orientation prop for vertical and horizontal lists
Wrapping - Includes usage of the wrapping prop
Grid - Shows how to build a grid of focus nodes
Disabled Focus Nodes - Shows how to disable focus nodes using the disabled prop
Focus Trap - Demonstrates how to create focus traps

Advanced Examples

Modal - Show and hide an animated modal overlay
Animated Page Transition - Animate between two pages
isExiting Page Transition - Animating between pages without user input
Pointer Events - An interface that supports both pointer and LRUD input
Grid That Remembers Position - A grid that returns you to your previous position when you exit and re-enter it
TV App - A simple TV app

Prior Art

"Pass the Remote" on the Netflix Tech Blog
bbc/lrud
react-tv
@xdproto/focus (the predecessor of this library)

@please/lrud

lrud

Motivation

Installation

Table of Contents

Guides

Basic Setup

Getting Started

FAQ

What is LRUD?

API Reference

<FocusRoot />

<FocusNode />

useFocusNodeById( focusId )

useLeafFocusedNode()

useActiveNode()

useSetFocus()

useNodeEvents( focusId, events )

useFocusHierarchy()

useProcessKey()

useFocusStoreDangerously()

Interfaces

FocusNode

LRUDEvent

MoveEvent

GridMoveEvent

FocusEvent

FocusStore

FocusState

Examples

Basic Examples

Advanced Examples

Prior Art

Readme

Keywords

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