These days, the term "react" is being bandied around a lot in the business. When it comes to front-end development, ReactJS is the most popular choice, and this lesson on how to answer ReactJS interview questions will help you get the job. Listed below are the most often requested ReactJS interview questions, from the most basic to the most complicated. Five frequently requested React interview questions are shown here: 1. Instead of Angular, why not use React instead It's simpler to construct dynamic web apps using React since it gives less coding and more functionality, but with JavaScript applications, the code tends to grow complicated very fast. Faster web apps due to the usage of virtual DOM in React applications. Instead of updating all of the components in the actual DOM, the virtual DOM analyzes its prior state and updates just those components that have changed. To put it another way, the building blocks of every React project may be re-used by creating new ones using components. To save down on development time, these pre-built components each contain their own logic and controls that may be shared throughout the program as a whole. There is one-way data flow via React, which is only one direction. As a result, we commonly layer child components inside their parent components in a React app's design process. It's also simpler to troubleshoot faults since data travels in a single channel, making it easier to pinpoint where the issue is in an application. Facebook has published a browser plugin that allows us to debug React apps more easily. Debugging React web apps is now quicker and simpler thanks to this improvement. 2. What do redux thunks serve? Using Redux thunk, you may build action creators that return functions instead of actions. An action may be delayed until a given condition is met by using the delay function. You may pass the two store methods getState and dispatch to the inner function. You must use the method first. This can be seen in the code below: applyMiddleware() import{ createStore, applyMiddleware } from 'redux'; 
import thunk from 'redux-thunk';
import rootReducer from './reducers/index';
const store = createStore(
  rootReducer,
  applyMiddleware(thunk) 
); 3. What does useState() in React do The React Hook allows state variables to be used in functional components. This approach is excellent for dynamically manipulating/controlling the DOM. useState() method is the second parameter of , which returns a tuple with count as the first argument and the setCounter method as the second. SetCounter UseState(0) ..
const [count, setCounter] = useState(0);
const [otherStuffs, setOtherStuffs] = useState(..); ..
const setCount = () => {
  setCounter(count + 1); 
  setOtherStuffs(..);
  ..
}; To update the count, use the method at any place. In this example, is utilized in the method, where a variety of different actions may be taken. When we utilize hooks, we may make our code more useful and avoid the need for class-based components if they aren't absolutely essential. setCounter() SetCounter() setCount 4. Is the useEffect hook useful The React Hook may be used to generate side effects in functional components. You may use to inform React that your component requires something to happen after it has been rendered or after a state change. useEffect useEffect React will remember and execute the function you provided it as soon as the DOM update performance is complete (also known as "effect"). In addition to updating the page title, this function may also be used to get data from the web server. The hook is automatically enabled after the component's first render and each subsequent update. Upon completion, the DOM will have been modified. useEffect Hooks for React. It's possible to with two arguments: useEffect useEffect(callback[, dependencies]); Callback 1 represents the function containing side-effect logic, which is called immediately after the DOM changes are applied. The second parameter's dependents array may be whatever you want it to be. will be invoked as long as the dependencies between renderings change. useEffect() import { useEffect } from 'react'; 
function WelcomeGreetings({ name }) {
  const msg = `Hi, ${name}!`; 
  useEffect(() => {
    document.title = `Welcome to you ${name}`; 
  }, [name]);
  return <div>{msg}</div>;
} A side-effect is anything that happens as a result of the previous code but isn't directly responsible for it. Consequently, now contains a callback for updating document titles (). useEffect You may need to specify the name as an effect dependency for useEffect if you want to avoid a document title change on the WelcomeGreetings component's presentation every time useEffect(callback, [name]) 5. Describe a few techniques for speeding up a React app Taking a look at some strategies to speed up a React project is a good place to start. Using the useMemo function () This React hook may be used to cache CPU-intensive tasks. For certain React apps, the continuous usage of CPU-intensive functions might result in the delayed rendering when a component is re-rendered. The hook may be used to cache such procedures. Only when it is absolutely essential should the CPU- intensive method be used. useMemo() useMemo() Maintaining a Cooperative State You want to get the state as close to your desired location as feasible. The parent component of React applications may include a large number of redundant states, making it more difficult to understand and manage the code. When there are many states in a single component, the whole thing re-renders. It's best to segregate states that aren't critical to the parent component. Let's get rid of the sluggish loading. Speeding up the startup of a React app using this technique. Lazy loading reduces the risk of web app performance problems to a minimum.

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