use-lazy-state

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Tiny useLazyState hook. Similar to useState, but giving you control over the re-rendering process. Subscribe to state changes in leaf components and don't re-render the entire component tree.

Install

npm i use-lazy-state

Demo

• Code Sandbox Examples

Usage

Simple state

import { useLazyState, UseLazyState } from 'use-lazy-state';

/**
 * Creating state. Parent component.
 * - You can declare state using `const state = useLazyState()`.
 * - To re-render the component when state chages, use the
 *   internal hook `state.useState()`.
 * - If `state.useState()` is not used, the component would not be
 *   re-rendered when the state changes.
 */

export function ParentNoRerender() {
  console.log('Rendering ParentNoRerender');

  // Changes in the isOpen state will not trigger a re-render of the Parent
  // because it is not using isOpen.useState()
  const isOpen = useLazyState(false);

  // isOpen.setState() would trigger a re-render on
  // any component using isOpen.useState()
  const onClick = () => isOpen.setState(prev => !prev);

  return (
    <div>
      <button onClick={onClick}>Toggle Open</button>
      <ChildUsingState isOpen={isOpen} />
    </div>
  );
}

/**
 * Subscribing to state changes. Child component.
 * - Opt-in all state changes with `state.useState()` or
 *   a particular part of the state using a getter
 *   `.useState((state) => state.whatever)`.
 * - Changes in the state are compared with === and the
 *   state change would only be triggered if a change
 *   is detected.
 */

function ChildUsingState(props: { isOpen: UseLazyState<boolean> }) {
  console.log('Rendering ChildUsingState');

  // Subscribe to state to get state updates
  const isOpen = props.isOpen.useState();

  // isOpen will change whenever an update to the state is triggered (compared with ===)
  if (!isOpen) return null;

  return <div>Opened</div>;
}

This would console.log the following:

Rendering ParentNoRerender
Rendering ChildUsingState

...after clicking the toggle button
Rendering ChildUsingState

Complex state (List)

import { useLazyState, UseLazyState } from 'use-lazy-state';

/**
 * Creating state. Parent component.
 * - You can declare state using `const state = useLazyState()`.
 * - To re-render the component when state chages, use the
 *   internal hook `state.useState()`.
 * - If `state.useState()` is not used, the component would not be
 *   re-rendered when the state changes.
 */

export function List() {
  console.log('Rendering List');

  // Declare state in the parent. Changes to the array
  // won't trigger a re-render in the parent because it
  // is not using `numberList.useState()`
  const numberList = useLazyState([0, 0, 0]);

  return (
    <div className="space-y-3">
      <ListItem numberList={numberList} indexToRender={0} />
      <ListItem numberList={numberList} indexToRender={1} />
      <ListItem numberList={numberList} indexToRender={2} />
    </div>
  );
}

/**
 * Subscribing to state changes. Child component.
 * - Opt-in all state changes with `state.useState()` or
 *   a particular part of the state using a getter
 *   `.useState((state) => state.whatever)`.
 * - Changes in the state are compared with === and the
 *   state change would only be triggered if a change
 *   is detected.
 */

type Props = {
  numberList: UseLazyState<number[]>;
  indexToRender: number;
};

function ListItem({ numberList, indexToRender }: Props) {
  console.log(`Rendering ListItem[${indexToRender}]`);

  const n = numberList.useState(
    // Getter. Get the full state object and return either the
    // full object or a part you want. Changes are compared
    // with === to prevent rendering if an object reference
    // did not change.
    numbers => numbers[indexToRender]
  );

  const addOne = () => {
    numberList.setState(
      // Setter. Get the full previous state object and
      // return the new full state.
      prev => {
        prev[indexToRender] = prev[indexToRender] + 1;

        // Create a new object because changes are compared with ===
        return [...prev];
      }
    );
  };

  return (
    <div>
      ListItem[{indexToRender}]: {n} <button onClick={addOne}>+1</button>
    </div>
  );
}

This would console.log the following:

Rendering List
Rendering ListItem[0]
Rendering ListItem[1]
Rendering ListItem[2]

...after clicking +1 on item ListItem[0]
Rendering ListItem[0]

...after clicking +1 on item ListItem[1]
Rendering ListItem[0]

...after clicking +1 on item ListItem[2]
Rendering ListItem[2]

API

useLazyState(initialState: T)

• Declare state object. Changes to the state would not trigger a re-render, unless you

subscribed to state changes with state.useState().

• Returns UseLazyState<T>

UseLazyState.useState(getter?: (state) => any)

• Subscribes the component to state changes
• Returns full state object or a part of the state using the getter

UseLazyState.setState()

• Call setState(newState) to set the full state object
• Alternatively, use a setter setState(prev => ({...prev, property: newValue})) to get

the latest full state value before updating the state.

• Changes to the state would not trigger a re-render on this component, unless you subscribed

the component to changes with .useState().

• Returns undefined (void)