Quando usar o useMemo e useCallback?
What is the usage of useMemo and useCallback
Fundamentally, useMemo and useCallback are tools built to help us optimize re-renders. They do this in two ways: Reducing the amount of work that needs to be done in a given render. Reducing the number of times that a component needs to re-render.
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What is the main difference between useMemo and useCallback
To summarize, the main difference between useCallback and useMemo is the type of value they return. useCallback returns a memoized callback function, while useMemo returns a memoized value.
What are the disadvantages of useCallback and useMemo
Every pro has a con, and one drawback is that excessive use of the useMemo and useCallback hooks could make your code less readable. Not only do they bloat the codebase, but you also have to actively maintain the dependencies array, because the value or function object might not update when you'd expect it to.
Should I use useCallback on every function
useCallback() "Every callback function should be memoized to prevent useless re-rendering of child components that use the callback function" is the reasoning of his teammates. This reasoning is far from the truth. Such usage of useCallback() without profiling makes the component slower and increases code complexity.
What is the benefit of using useCallback
One reason to use useCallback is to prevent a component from re-rendering unless its props have changed. In this example, you might think that the Todos component will not re-render unless the todos change: This is a similar example to the one in the React.memo section.
Why are callback functions used
We need callback functions because many JavaScript actions are asynchronous, which means they don't really stop the program (or a function) from running until they're completed, as you're probably used to. Instead, it will execute in the background while the rest of the code runs.
What is the disadvantage of useCallback
Drawbacks of React useCallback
Memory allocation: Similar to garbage collection, the more memoized functions you have, the more memory that'll be required. Plus, each time you use these callbacks, there's a bunch of code inside React that needs to use even more memory to provide you with the cached output.
What are the cons of useMemo
Pros and cons of using useMemo
| useMemo pros | useMemo cons |
|---|---|
| Helps developers cache a value to avoid unwanted costly recalculations | Adds excessive syntax for compute function calls, so use of useMemo may complicate your code |
When would you use a callback function
A callback's primary purpose is to execute code in response to an event. These events might be user-initiated, such as mouse clicks or typing. With a callback, you may instruct your application to "execute this code every time the user clicks a key on the keyboard." button.
What is the benefit of useMemo
The useMemo Hook in React is a performance optimization tool that allows you to memoize expensive computations and avoid unnecessary re-renders.
What is a real life example of callback function
Another real-world example of using a callback function is when fetching data from a server. In this case, we use a callback function to handle the data once it has been received.
Where does callback function use
A callback function is a function passed into another function as an argument, which is then invoked inside the outer function to complete some kind of routine or action.
What is the downside of useMemo
useMemo itself requires memory so if we are trying to over-optimize by memoizing every function, it might slow the application down. We should also not use useMemo when the function returns a primitive value, such as a boolean or a string.
What are the cons of useCallback
Pros and cons of using useCallback
| useCallback pros | useCallback cons |
|---|---|
| Helps developers cache a function to avoid excessive re-renders of a child component | Adds excessive syntax for callback definition, so use of useCallback may complicate your code |
What is the advantage of callback function
The benefit of using a callback function is that you can wait for the result of a previous function call and then execute another function call. In this example, we are going to use the setTimeout() method to mimic the program that takes time to execute, such as data coming from the server.
What is the difference between callback and callback function
A callback is a function passed as an argument of another function. This means that the parent function is usually built to use any kind of function. But the callback function, on the other hand, is meant to be used in a specific case (or a restricted number of cases) in which the parent function is used.
What is the benefit of useCallback
Why useCallback is Used It is useful when passing callbacks to optimized child components that rely on reference equality to prevent unnecessary renders. Simple, the usecallback hook is used when you have a component in which a child is rendering repeatedly without the need for it.
What is use callback for
useCallback is a hook that will return a memoized version of the callback function that only changes if one of the dependencies has changed. Memoization is a way to cache a result so that it doesn't need to be computed again. This can boost performance.
Why do we need callback functions
Need for Callback Functions
This is called asynchronous programming. We need callback functions to make sure that a function is only going to get executed after a specific task is completed and not before its completion.
What is the downside of using useMemo
useMemo itself requires memory so if we are trying to over-optimize by memoizing every function, it might slow the application down. We should also not use useMemo when the function returns a primitive value, such as a boolean or a string.
What are the disadvantages of callback functions
The main disadvantage of callbacks is known to every developer as callback hell and looks always more or less as illustrated below. In the image, there is a block of code with nested callback functions where each of them calls the next callback and depends on the previous one.
What is the drawback of callback
So, it is quite evident that the presence of callbacks in the code makes it harder to maintain or further write the code. It poses a hurdle in understanding the flow of code and is a major drawback when debugging the entire code.
What are the two types of callbacks
There are two types of callbacks, differing in how they control data flow at runtime: blocking callbacks (also known as synchronous callbacks or just callbacks) and deferred callbacks (also known as asynchronous callbacks).
What is the use of useMemo
The useMemo Hook can be used to keep expensive, resource intensive functions from needlessly running. In this example, we have an expensive function that runs on every render. When changing the count or adding a todo, you will notice a delay in execution.
What is the practical use of callback
Callbacks make sure that a function is not going to run before a task is completed but will run right after the task has completed. It helps us develop asynchronous JavaScript code and keeps us safe from problems and errors.