@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

``ts
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.

$3

`jsx
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

`ts
function useConst(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.

$3

`jsx
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(/.../);
...
};
`

$3

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

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

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

type ChangeCallback = (
ev: React.FormEvent | 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

`ts
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

`ts
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.

$3

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

const TextField = ({ labelText, defaultValue }) => {
const id = useId('field');
return (



);
};
`

useMergedRefs

`ts
function useMergedRefs(...refs: React.Ref[]): (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.

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

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

return

;
});
`

useOnEvent

`ts
function useOnEvent(
element: React.RefObject | 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

`ts
function usePrevious(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

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

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

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.

$3

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

const MyComponent = () => {
const myDivRef = useRefEffect(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