Memoization is an optimization approach, just like caching. It really works by storing the earlier outcomes of a operate name and utilizing these outcomes the subsequent time the operate runs. It’s particularly helpful in computation-heavy apps that repeat operate calls on the identical parameters.
Whenever you name this operate, it first checks whether or not the result’s current within the cache earlier than working. Whether it is, it returns the cached outcomes. In any other case, it executes.
Think about this operate:
return num * num
The operate takes in an argument and returns its sq..
To run the operate, name it with a quantity like this:
With 5 because the argument, sq.() will run fairly quick. Nevertheless, for those who had been to calculate the sq. of 70,000, there can be a noticeable delay. Not by a lot however a delay nonetheless. Now, for those who had been to name the operate a number of instances and move 70,000, you’ll expertise a delay in every name.
You possibly can eradicate this delay utilizing memoization.
const memoizedSquare = () =>
let cache = ;
return (num) =>
if (num in cache)
console.log('Reusing cached worth');
let consequence = num * num;
// cache the new consequence worth for subsequent time
cache[num] = consequence;
On this instance, the operate checks whether or not it’s computed the consequence earlier than, by checking if it exists within the cache object. If it has it returns the already computed worth.
When the operate receives a brand new quantity, it calculates a brand new worth and shops the ends in the cache earlier than it returns.
Once more this instance is fairly easy, but it surely explains how memoization would work to enhance the efficiency of a program.
It is best to solely memoize pure capabilities. These capabilities return the identical consequence while you move the identical arguments in. In the event you use memoization on impure capabilities, you’ll not enhance efficiency however enhance your overhead. That is since you select velocity over reminiscence each time you memoize a operate.
Memoization in React
In case you are trying to optimize React elements, React gives memoization by means of the useMemo() hook, React.memo, and useCallBack().
useMemo() is a React hook that accepts a operate and a dependency array.
const memoizedValue = useMemo(() => computeExpensiveValue(a, b), [a, b]);
It memoizes the worth returned from that operate. The values within the dependency array dictate when the operate is executed. Solely after they change is the operate executed once more.
For instance, the next App part has a memoized worth referred to as consequence.
import useMemo from "react"
const sq. = (worth) =>
return worth * worth
const consequence = useMemo(
() => sq.(worth),
[ value ]
The App part calls sq.() on each render. The efficiency will degrade if the App part is rendered many instances as a result of React props altering or state updating, particularly if the sq.() operate is dear.
Nevertheless, since useMemo() caches the returned values, the sq. operate just isn’t executed in every re-render until the arguments within the dependency array change.
React.memo() is the next order part that accepts a React part and a operate as arguments. The operate determines when the part ought to be up to date.
The operate is non-obligatory and if not supplied, React.memo makes a shallow copy comparability of the part’s present props to its earlier props. If the props are totally different, it triggers an replace. If the props are the identical, it skips the re-render and reuses the memoized values.
The non-obligatory operate accepts the earlier props and the subsequent props as arguments. You possibly can then explicitly examine these props to resolve whether or not to replace the part or not.
React.memo(Element, [areEqual(prevProps, nextProps)])
Let’s have a look at an instance with out the non-obligatory operate argument first. Under is a part referred to as Feedback that accepts the title and e mail props.
operate Feedback (title, remark, likes)
The memoized feedback part can have React.memo wrapped round it like this:
const MemoizedComment = React.memo(Remark)
You possibly can name then name it like another React part.
<MemoizedComment title="Mary" remark="Memoization is nice" likes=1/>
If you wish to carry out the props comparability your self, move the next operate to React.memo because the second argument.
import React from "react"
operate checkCommentProps(prevProps, nextProps)
return prevProps.title === nextProps.title
&& prevProps.remark === nextProps.remark
&& prevProps.likes === nextProps.likes
const MemoizedComment = React.memo(Feedback, checkCommentProps)
If checkProfileProps returns true, the part just isn’t up to date. In any other case, it’s re-rendered.
The customized operate is helpful while you need to customise the re-render. For instance, you may use it to replace the Feedback part solely when the variety of likes modifications.
In contrast to the useMemo() hook that memoizes solely the returned worth of a operate, React.memo memoizes the entire operate.
Use React.memo just for pure elements. Additionally, to cut back comparability prices, solely memoize elements whose props change typically.
You should utilize the useCallBack() hook to memoize function components.
const memoizedCallback = useCallback(
The operate will get up to date solely when the values within the dependency array change. The hook works just like the useMemo() callback, but it surely memoizes the operate part between renders as an alternative of memoizing values.
Think about the next instance of a memoized operate that calls an API.
import useCallback, useEffect from "react";
const Element = () =>
const getData = useCallback(() =>
console.log('name an API');
The getData() operate referred to as in useEffect will probably be referred to as once more solely when the getData worth modifications.
Ought to You Memoize?
React 18 additionally launched new hooks like useId, useTransition, and useInsertionEffect. You should utilize these to enhance the efficiency and consumer expertise of React purposes.