MERN Stack Interview Questions

Ans.

State is a built-in object that allows components to manage and respond to dynamic data or user input.

• Unlike props, which are immutable and passed down from parent to child, state is local to the component and can be changed using the setState method in class components or the useState hook in functional components.
• When the state changes, React re-renders the component to reflect the new state.

Example using useState in a functional component:

import React, { useState } from 'react';

function Counter() {
const [count, setCount] = useState(0);

return (
<div>
<p>You clicked {count} times</p>
<button onClick={() => setCount(count + 1)}>
Click me
</button>
</div>
);
}

• In this example, count is a state variable initialized to 0, and setCount is the function used to update it.

Ans.

React Router is a library for handling navigation in React applications. It enables dynamic routing without reloading the page.

Example:

import { BrowserRouter as Router, Route, Switch } from "react-router-dom";

function App() {
return (
<Router>
<Switch>
<Route path="/" exact component={Home} />
<Route path="/about" component={About} />
</Switch>
</Router>
);
}

• Here, Switch ensures only one route renders at a time.