What is the useCallback hook, and why is it used?

The useCallback hook of React is applied to memoize a call function, that is, to save the function instance such that the same function instance is returned by the hook between component renders, provided the dependencies of the function do not change. This averts reconstruction of this functional possibility on each render.

The main reason behind using useCallback is to maximize the performance through avoiding unnecessary child components re-rendering because of receiving callback functions as props. In the absence of useCallback, each re-rendering of a parent component would instantiate new copies of the callback functions and send them to child components, which would in turn re-render unnecessarily as the functions they receive (via their props) have altered due to reference change.

useCallback is most commonly used in the following form:

js

const memoizedCallback = useCallback(() => {

  // Function logic here

}, [dependencies]);

• In the first render, it gives the original function.
• On later renders, it caches the function again unless there are any dependency changes in which case it caches a new function.

UseCallback has the following benefits:

• Efficiency optimization through the process of avoiding children re-renders of unnecessary children.
• Clearly defined time of recreation of the callbacks through listing dependencies.
• Better readability of its code through indication of stable references of functions.

Nevertheless, useCallback may lead to code proliferation and memory consumption when it is misused and therefore is not applied to every function, but to those functions where a re-rendering that is expensive is an issue when it is reused as a prop.

In short, useCallback allows preserving the referential integrity of functions between renders and ensures that child components do not need to be re-rendered unnecessarily, and helps improve the performance of React apps.