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>
);

PropagationScope

The PropagationScope component allows you to create isolated scopes for propagation. This is useful when you want to limit the scope of propagation to a specific part of your component tree.

Here's an example of how to use PropagationScope:

import { createPropagation } from 'use-propagate';

const { useListen, usePropagate, PropagationScope } = createPropagation<string>();

const ParentComponent = () => {
  return (
    <div>
      <PropagationScope>
        <ChildComponent1 />
        <ChildComponent2 />
      </PropagationScope>
      <ChildComponent3 />
    </div>
  );
};

const ChildComponent1 = () => {
  const propagate = usePropagate();
  
  return <button onClick={() => propagate('Hello')}>Say Hello</button>;
};

const ChildComponent2 = () => {
  useListen((message) => {
    console.log('ChildComponent2 received:', message);
  });

  return <div>Child 2</div>;
};

const ChildComponent3 = () => {
  useListen((message) => {
    console.log('ChildComponent3 received:', message);
  });

  return <div>Child 3</div>;
};

In this example:

• ChildComponent1 and ChildComponent2 are wrapped in a PropagationScope.
• When the button in ChildComponent1 is clicked, it will propagate the message "Hello".
• ChildComponent2 will receive this message and log it.
• ChildComponent3, which is outside the PropagationScope, will not receive the message.

Using PropagationScope allows you to create multiple isolated propagation contexts within your application. This can be particularly useful in larger applications where you want to avoid unintended propagation between different parts of your component tree.

Note that useListen and usePropagate will use the nearest PropagationScope in the component tree. If there's no PropagationScope ancestor, they will use a default global scope.

API

export function createPropagation<T>(options?: { allowPropagateDuringRender?: boolean }): {
  PropagationScope: React.ComponentType<{ children?: React.ReactNode | undefined }>;
  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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