`use-propagate`

Propagates a value to multiple nodes via callback function using React context and hooks.

Background

This pattern is useful for triggering multiple nodes via callback function.

Unlike setting a value in a context, invoking a callback function will not trigger re-render. Subscribers can choose to save the value into its state and re-render as needed.

How to use

Live demo

The following code snippet sends the focus to the text box when the button is tapped.

import { createPropagation } from 'use-propagate';

// Creates a namespace for the propagation. This should be placed outside of the component.
const { useListen, usePropagate } = createPropagation<void>();

const FocusButton = () => {
  const propagate = usePropagate();

  // When tapped, it will trigger all subscribers.
  const handleClick = useCallback(() => propagate(), [propagate]);

  return (
    <button autoFocus={true} onClick={handleClick}>
      Tap to focus to the text box
    </button>
  );
};

const TextBox = () => {
  const ref = useRef<HTMLInputElement>(null);

  // When the callback is called, send the focus to the text box.
  const handleListen = useCallback(() => ref.current?.focus(), [ref]);

  // Listens to the propagation.
  useListen(handleListen);

  return <input ref={ref} type="text" />;
};

render(
  <Fragment>
    <FocusButton />
    <TextBox />
  </Fragment>
);

API

export function createPropagation<T>(): {
  useListen: (callback: (value: T) => void) => void;
  usePropagate: (value: T) => void;
};

Behaviors

Why not passing values via `useContext`?

When propagating a value via useContext, subscribing nodes will be re-rendered. This behavior may not be desirable for events and certain type of scenarios.

Why I should not call propagate callback function during render-time?

When the propagate callback function is called during rendering, a warning message will be printed and propagation will be stopped.

This is a safety measure to prevent multiple re-render and potential deadlock situation if listeners save the value to a state and trigger another re-render.

If listeners are controlled and would never trigger re-render, you can pass allowPropagateDuringRender: true option to ignore this safety measure.

How to get response from the listener or wait for the listener to complete?

Modifies the passing value by following the FetchEvent.respondWith or ExtendableEvent.waitUntil pattern.

How to re-render when triggered?

Use the following code snippet to save the value to a state, which will re-render the component.

const MyComponent = () => {
  const [value, setValue] = useState<number>();

  // When triggered, saves the value to state.
  useListen(setValue);

  return <p>The value is {value}.</p>;
};

Please make sure the propagate callback function is not called during render as it could cause multiple re-render and potential deadlock situation.

Contributions

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compulim/use-propagate

use-propagate