collect provided arguments; compare arguments with the ones provided in previous call (=== React has a built-in hook called useMemo that allows you to memoize expensive functions so that you can avoid calling them on every render. Using memoize in a react app useMemo, React.memo, and createSelector are usually enough for all your memoization needs. Adapting useMemo to our use case: In fact, you can use the useRef to keep reference to an expensive function evaluation — so long as the function doesn’t need to be recomputed on props change. Note: React.memo and React.useMemo uses the same technique for optimization but there use cases differs. Whenever we want to memoize a function: function toBeMemoed(input In useMemo there are many mistakes devs new to it usually make. const longOp = memoize((input) => ... React will re-compute the memoizedFunc to get the new value, with that React smartly avoids expensive function executing on every render with thtw same input as the previously seen one. memo (function MyComponent (props) {// only renders if props have changed}); This is a performance boost since only the things that need to be rendered are rendered. The proxy-memoize library provides a memoize function. Just to highlight: useMemo hook is rather for preserving referential equality (say, if some function returns an array or an object than calling that function on each render would provide referentially different result on each run). The syntax for this hook is actually the exact same as useEffect since they both work in a similar way. React comes with an awesome HoC: React.memo that allows us to memoize function components: // When we use the HoC without supplying a comparation function it // will shallowly compare the props of the component to determine // if it calls the render function const MemoizedComponent = React. Trite Example: function add(a, b) { return a + b; } add(20, 5); add(10, 10); add(20, 5); add(10, 10); add(20, 5); If add were a really slow function, your app would needlessly come to a crawl. The first argument of useMemo is a function that does the complex calculation you want to memoize, and the second argument is an array of all dependencies for that memoization. We would memoize the longOp function with the memoize function. Both libraries return a function which accepts a given numbers of arguments and returns a value:. Function Components. React.memo is used on components only but useMemo can be used on both components and standalone functions. Memoize effectively lets you cache the results of a function for the same arguments. The library exports two main functions… useRef is the right Hook for such scenarios, NOT the useMemo Hook. You simple pass in a function and an array of inputs and useMemo will only recompute the memoized value when one of the inputs has changed. const ToTheMoonComponent = React. It will take a function and return a memoized function. One implementation is described in the react docs. React… getA(arg1, arg2, arg3) // Returns a value The difference lays in what happens under the hoods when the function is called.. memoize-one. function Bla() { const { current: baz } = useRef([1, 2, 3]) return } Problem solved. However hooks don't work in class components. PureComponent works with classes. The most basic form of memoization in React is the useMemo hook. If you still have some in your codebase, you need a custom memoization function to replicate the functionality of useMemo. 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