React useMemo Guides
useMemo returns a memoized value so that it does not need to be recalculated.
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When I start to write this blog, I ask myself whether I should only talk about the differences between useMemo and useCallback because they are React Hooks while React.memo is not. Eventually, I decided to include React.memo as well since on the one hand the word
memoin both terminologies might sound a bit confusing for people. On the other hand, it's all about React optimization 😁
Today we will talk about when to useCallback and useMemo React hooks in our projects.
In the above section, we looked at what
useCallbackhook is and how to use it. It is now time to look at another hook closely related to
useMemo. The function signature of
useMemois similar to that of
useCallback. The difference is that
useMemoreturns a memoized value while
memoizedcallback function. Both take a function as first argument and an array of dependencies as second argument.
useMemohook is used for performing operations which are computationally expensive (Takes a long time to perform or a lot of computer memory). If the dependencies do not change,
memoizedvalue will always be returned. If you want the computation to be performed once then pass an empty array.
In this article we will look at two react hooks
useCallback, which will bring us to look at when React renders components.
We will look only at function-based components and not class-based components. (I am not familiar with such class-based components).
There are 3 possible options to create a constant in React:
useRef. We're going to see which one is the best way to create real constants (not constant-like values).
Here, Form gets executed only when selectedUser changes, so the expression need not be evaluated every time. This method allows us to optimise the expression evaluation as switch needs to execute it every time but useMemo doesn't.
There comes a time when we have to worry about more than just making sure our applications work, but that they work optimally. When using react, we have certain tools at our disposal to make sure our applications are optimised. In this article, I will demonstrate how to achieve this using React.memo and the useMemo hook.
Performance is important, especially in large-scale application. The React useMemo hook is one tool you can use to improve the performance of your React apps. This tutorial will help you understand what useMemo hook is and how it works. It will also show you how to use it.
As we can see, the WelcomeCard is rendered again everytime we click on the counter, in fact it is rendered more times than the counter. This is happening even though there is nothing that is dynamic inside the card itself, thus the re-rendering is a waste. Now imagine a website with lots of static data components, which re-render everytime states or states of parents change. To avoid this we can use useMemo as follows:-
In the example above, we used
ItemComponent1. Thus anything returns the component will be initialized only once. It won't be re-rendered at the time of parent re-rendering.
Hooks are relatively new feature of react, they were introduced in React 16.8, they help us make use of state and react features from a function based component, for example useState, useEffect, useHistory and many others. Hooks help us to avoid the complexities of classes and make our code simpler to read and understand.
In this article, we will go about the useMemo hook in React. In addition to understanding the functionality of this hook, it is also important to note that this hook has its importance from react interview perspective since many interviewers like to ask questions related to useMemo hook.
If you’re not completely new to React, you’re probably already at least familiar with useMemo and useCallback hooks. And if you work on a medium to large-scale application, chances are you can describe some parts of your app as an “incomprehensible chain of
useCallbacks that is impossible to read and debug". Those hooks somehow have the ability to just spread around the code uncontrollably, until they just completely take over and you find yourself writing them just because they are everywhere and everyone around you is writing them.
Tip 2: Because of the use of shallow comparison, be careful about passing in non-primitive props like an object, array or function. Do not pass these in directly as props, but instead, instantiate and assign these to variables which are then passed in. For functions, the
useCallbackhook is handy for ensuring the same instance of the function is passed in as props, thus allowing the shallow prop comparison to result in
true. For objects and arrays, the
useMemohook might be helpful, which I'll go through in the next section.
Hi, I quite often use this syntax to render my components conditionally and I've got a lot of review about this to not use
useMemoto render markups. Is it wrong doing it this way?
These two React hooks,
useCallbackare useful when you’re dealing with expensive operations (that is, operations that are very complex and take a lot of time and resources, like CPU.)
Happy React useMemo coding!