React.js ~The Latest Ref Pattern ~
This pattern holds callback passed to a customhook in the ref and update existing value everytime rendered to have the latest value. function useDebounce ( callback , delay ) { const callbackRef = React . useRef ( callback ) React . useLayoutEffect (() => { callbackRef . current = callback }) return React . useMemo ( () => debounce ((... args ) => callbackRef . current (... args ), delay ), […
The latest Ref pattern in React is a technique that allows you to pass a callback to a custom hook and update its value every time the component is rendered, ensuring you always have the most recent value. This pattern was introduced by Yago Pereria.
The main reason for using the Ref is to maintain a current value without triggering a re-render, which would otherwise lead to an infinite loop. By holding values in state, the component re-renders every time the value changes, causing an endless loop.
In the second part of the article, the focus is on dealing with Dependency Arrays. While it's necessary to follow the exhaustive-deps rule, you should not include the current value of a Ref in the Dependency Array. Since updating the Ref does not trigger a re-render, React cannot detect any changes to the current value, leading to issues in debugging.
React 19 introduced the useEffectEvent, which is specifically designed to incorporate this pattern into the official API. With React 19, there might be situations where creating a handwritten "latest Ref" is no longer required.
Callbacks in React are updated every time the component renders, as a new instance of the function is created with each render. This means that even if the function appears only once in the source code, a new instance is created with every render.
A common example is a debounce function that filters API calls based on user input. Although the arrow function appears only once in the source code, a new instance is created every time the component is rendered. As query changes with every input, it effectively becomes a "different function" with every keystroke. If you hold onto the function generated in the first render, the function that runs is the function that watches the initial query and keeps searching for an empty string, causing a classic "stale closure" bug.
Instead of adding the callback to the Dependency Array, which would cause the debounced instance to be recreated and discard pending timers, using a Ref is a better approach. This way, you can maintain both a stable instance of debounce and an up-to-date function.
In summary, the latest Ref pattern is a useful technique in React for updating values without triggering unnecessary re-renders while ensuring that callbacks remain current. This pattern is particularly helpful when dealing with Dependency Arrays and managing stale closures.
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