@uifabric/react-hooks

Fluent UI React hooks

Helpful hooks not provided by React itself. These hooks were built for use in Fluent UI React (formerly Office UI Fabric React) but can be used in React apps built with any UI library.

• useBoolean - Return a boolean value and callbacks for setting it to true or false, or toggling
• useConst - Initialize and return a value that's always constant
• useControllableValue - Manage the current value for a component that could be either controlled or uncontrolled
• useForceUpdate - Force a function component to update
• useId - Get a globally unique ID
• useMergedRefs - Merge multiple refs into a single ref callback
• useOnEvent - Attach an event handler on mount and handle cleanup
• usePrevious - Get a value from the previous execution of the component
• useRefEffect - Call a function with cleanup when a ref changes. Like useEffect with a dependency on a ref.
• useSetInterval - Version of setInterval that automatically cleans up when component is unmounted
• useSetTimeout - Version of setTimeout that automatically cleans up when component is unmounted
• useTarget - Logic used by several popup components to determine the target element or point to position against
• useWarnings - Display debug-only warnings for invalid or deprecated props or other issues

useBoolean

function useBoolean(initialState: boolean): [boolean, IUseBooleanCallbacks];

interface IUseBooleanCallbacks {
  setTrue: () => void;
  setFalse: () => void;
  toggle: () => void;
}

Hook to store a boolean state value and generate callbacks for setting the value to true or false, or toggling the value.

The hook returns a tuple containing the current value and an object with callbacks for updating the value.

Each callback will always have the same identity.

Example

import { useBoolean } from '@uifabric/react-hooks';

const MyComponent = () => {
  const [value, { setTrue: showDialog, setFalse: hideDialog, toggle: toggleDialogVisible }] = useBoolean(false);
  // ^^^ Instead of:
  // const [isDialogVisible, setIsDialogVisible] = React.useState(false);
  // const showDialog = React.useCallback(() => setIsDialogVisible(true), []);
  // const hideDialog = React.useCallback(() => setIsDialogVisible(false), []);
  // const toggleDialogVisible = isDialogVisible ? setFalse : setTrue;

  // ... code that shows a dialog when a button is clicked ...
};

useConst

function useConst<T>(initialValue: T | (() => T)): T;

Hook to initialize and return a constant value. Unlike React.useMemo, this will always return the same value (and if the initializer is a function, only call it once). This is similar to setting a private member in a class constructor.

Its one parameter is the initial value, or a function to get the initial value. Similar to useState, only the first value/function passed in is respected.

If the value should ever change based on dependencies, use React.useMemo instead.

Example

import { useConst } from '@uifabric/react-hooks';

const MyComponent = () => {
  const value = useConst(() => {
    /* some computation that must only run once or has side effects */
  });
  const valueThatMustNeverChange = useConst(/*...*/);
  ...
};

Why not just useMemo?

According to the React docs:

You may rely on useMemo as a performance optimization, not as a semantic guarantee. In the future, React may choose to “forget” some previously memoized values and recalculate them on next render, e.g. to free memory for offscreen components. Write your code so that it still works without useMemo — and then add it to optimize performance.

In cases where the value must never change, the recommended workaround is to store it with useRef, but refs are more awkward to initialize and don't enforce or even communicate that the value should be immutable. An alternative workaround is const [value] = useState(initializer), but this is semantically wrong and more costly under the hood.

useControllableValue

// Without onChange
function useControllableValue<TValue, TElement extends HTMLElement>(
  controlledValue: TValue | undefined,
  defaultUncontrolledValue: TValue | undefined,
): Readonly<[TValue | undefined, (update: React.SetStateAction<TValue | undefined>) => void]>;

// With onChange
function useControllableValue<
  TValue,
  TElement extends HTMLElement,
  TCallback extends ChangeCallback<TElement, TValue> | undefined
>(
  controlledValue: TValue | undefined,
  defaultUncontrolledValue: TValue | undefined,
  onChange: TCallback,
): Readonly<
  [TValue | undefined, (update: React.SetStateAction<TValue | undefined>, ev: React.FormEvent<TElement>) => void]
>;

type ChangeCallback<TElement extends HTMLElement, TValue> = (
  ev: React.FormEvent<TElement> | undefined,
  newValue: TValue | undefined,
) => void;

Hook to manage the current value for a component that could be either controlled or uncontrolled, such as a checkbox or input field. (See the React docs about the distinction between controlled and uncontrolled components.)

Parameters:

• controlledValue (required): the current value if the component is controlled
• defaultUncontrolledValue (required): the default value if the component is uncontrolled (will not be used if controlledValue is defined)
• onChange (optional): callback to be notified of any changes triggered by the user

The returned value is an array with two elements:

• The current value
• A function that will update the internal state if uncontrolled, and invoke the onChange callback if present.
  • Like the setter returned by React.useState, the identity of this callback will never change.
  • Also like React.useState, you can call this function with either a value, or an updater function which takes the previous value as a parameter and returns the new value.

useForceUpdate

function useForceUpdate(): () => void;

Returns a function which, when called, will force update a function component by updating a fake state value.

The returned function always has the same identity.

useId

function useId(prefix?: string): string;

Hook to generate a unique ID (with optional prefix) in the global scope. This will return the same ID on every render.

Useful for cases in which a component may be rendered multiple times on the same page and needs to use an ID for internal purposes, such as associating a label and an input.

Example

import { useId } from '@uifabric/react-hooks';

const TextField = ({ labelText, defaultValue }) => {
  const id = useId('field');
  return (
    <div>
      <label htmlFor={id}>{labelText}</label>
      <input id={id} type="text" defaultValue={defaultValue} />
    </div>
  );
};

useMergedRefs

function useMergedRefs<T>(...refs: React.Ref<T>[]): (instance: T) => void;

Hook to merge multiple refs (such as one passed in as a prop and one used locally) into a single ref callback that can be passed on to a child component.

const Example = React.forwardRef(function Example(props: {}, forwardedRef: React.Ref<HTMLDivElement>) {
  const localRef = React.useRef<HTMLDivElement>();
  const mergedRef = useMergedRef(localRef, forwardedRef);

  React.useEffect(() => {
    localRef.current.focus();
  }, []);

  return <div>Example</div>;
});

useOnEvent

function useOnEvent<TElement extends Element, TEvent extends Event>(
  element: React.RefObject<TElement | undefined | null> | TElement | Window | undefined | null,
  eventName: string,
  callback: (ev: TEvent) => void,
  useCapture?: boolean,
): void;

Attach an event handler on mount and handle cleanup. The event handler is attached using on() from @uifabric/utilities.

usePrevious

function usePrevious<T>(value: T): T | undefined;

Hook keeping track of a given value from a previous execution of the component the Hook is used in. See React Hooks FAQ.

useRefEffect

function useRefEffect<T>(callback: (value: T) => (() => void) | void, initial: T | null = null): RefCallback<T>;

type RefCallback<T> = ((value: T | null) => void) & React.RefObject<T>;

Creates a ref, and calls a callback whenever the ref changes to a non-null value. The callback can optionally return a cleanup function that'll be called before the value changes, and when the ref is unmounted.

The return value is a function that should be called to set the ref's value. The returned object also has a .current member that can be used to access the ref's value (like a normal RefObject). This can be hooked up to an element's ref property.

useRefEffect can be used to work around a limitation that useEffect cannot depend on ref.current.

Example

import { useRefEffect } from '@uifabric/react-hooks';

const MyComponent = () => {
  const myDivRef = useRefEffect<HTMLElement>(myDiv => {
    const observer = new ResizeObserver(entries => {
      console.log(`myDiv is ${entries[0].contentRect.width} px wide`);
    });
    observer.observe(myDiv);

    // Return a function to clean up the ResizeObserver when the ref is unmounted
    return () => observer.disconnect();
  });

  return <div ref={myDivRef} />;
};

useSetInterval

function useSetInterval(): {
  setInterval: (callback: () => void, duration: number) => number;
  clearInterval: (id: number) => void;
};

Hook which returns safe setInterval and clearInterval methods. Intervals set up using this hook will be automatically cleared when the component is unmounted.

The returned callbacks always have the same identity.

Example

import { useSetInterval } from '@uifabric/react-hooks';

const MyComponent = () => {
  const { setInterval, clearInterval } = useSetInterval();

  // Set an interval
  const id = setInterval(() => console.log('test'), 500);

  // If needed, clear an interval manually.
  clearInterval(id);
};

useSetTimeout

function useSetTimeout(): {
  setTimeout: (callback: () => void, duration: number) => number;
  clearTimeout: (id: number) => void;
};

Hook which returns safe setTimeout and clearTimeout methods. Timeout callbacks set up using this hook will be automatically cleared when the component is unmounted.

The returned callbacks always have the same identity.

Example

import { useSetTimeout } from '@uifabric/react-hooks';

const MyComponent = () => {
  const { setTimeout, clearTimeout } = useSetTimeout();

  // Set a timeout
  const id = setTimeout(() => console.log('test'), 500);

  // If needed, clear an timeout manually.
  clearTimeout(id);
};

useTarget

type Target = Element | string | MouseEvent | Point | null | React.RefObject<Element>;

function useTarget<TElement extends HTMLElement = HTMLElement>(
  target: Target | undefined,
  hostElement?: React.RefObject<TElement | null>,
): Readonly<[React.RefObject<Element | MouseEvent | Point | null>, React.RefObject<Window | undefined>]>;

Hook which queries the document for the element indicated by a CSS query string (if provided), or returns the element/event/point provided. Also attempts to determine the Window object for the provided target.

useWarnings

function useWarnings<P>(options: IWarningOptions<P>): void;

Display console warnings when certain conditions are met. If using webpack, the warning code will automatically be stripped out in production mode.

The following types of warnings are supported (see typings for details on how to specify all of these):

• other: Generic string messages.
• conditionallyRequired: Warns about props that are required if a condition is met.
• deprecations: Warns when deprecated props are being used.
• mutuallyExclusive: Warns when two props which are mutually exclusive are both being used.
• controlledUsage: Warns on any of the following error conditions in a form component (mimicking the warnings React gives for these error conditions on an input element):
  • A value prop is provided (indicated it's being used as controlled) without a change handler, and the component is not read-only
  • Both the value and default value props are provided
  • The component is attempting to switch between controlled and uncontrolled

Note that all warnings except controlledUsage will only be shown on first render. New controlledUsage warnings may be shown later based on prop changes. All warnings are shown synchronously during render (not wrapped in useEffect) for easier tracing/debugging.

Deprecated hooks

useConstCallback

This hook was intended for creating callbacks which have no dependencies, and therefore never need to change. It works fine if everyone using it is extremely mindful of how closures work, but that's not a safe assumption--so in practice, usage of this hook tends to result in bugs like unintentionally capturing the first value of a prop and not respecting updates (when updates should be respected).

If absolutely necessary, you can imitate useConstCallback's behavior with useConst: const myCallback = useConst(() => () => { /* callback body */ }). (The extra function wrapper is necessary to prevent the callback itself from being interpreted as an initializer.)