Question 1

What is the main difference between let and var in JavaScript?

Accepted Answer

let has block scope while var has function scope. This means a variable declared with let is only accessible within the block where it's defined (between curly braces), whereas var is accessible throughout the entire function. This difference is crucial to avoid bugs related to hoisting and variables leaking outside their intended context.

Question 2

What is JSX in React?

Accepted Answer

JSX is a syntactic extension of JavaScript that allows writing HTML-like code directly within JavaScript. It gets transpiled into React.createElement() function calls by tools like Babel. JSX makes the code more readable and facilitates UI creation by combining logic and rendering in the same file.

Question 3

What is the basic component used to create containers in React Native?

Accepted Answer

The View component is the fundamental container in React Native, equivalent to a div in HTML. It allows grouping other components, applying styles, and managing layout via Flexbox. Unlike web, React Native uses View instead of div because it must be translated to native components (UIView on iOS, android.view on Android).

Question 4

Which function allows declaring a state variable in a React functional component?

Accepted Answer

useState is the fundamental hook for managing local state in functional components. It returns an array containing the current state value and a function to update it. Unlike class components that use this.state, functional components use useState for each independent state variable.

Question 5

What is the native JavaScript method for making HTTP requests in React Native?

Accepted Answer

fetch is the native API built into JavaScript and React Native for making HTTP requests. It returns a Promise and allows handling GET, POST, PUT, DELETE requests without external dependencies. Unlike axios, fetch is available natively without installing any package.

Question 6

What is the main characteristic of AsyncStorage in React Native?

Accepted Answer

AsyncStorage is an asynchronous, unencrypted, persistent key-value storage system. It works globally across the app and stores data as strings. It's the simplest storage solution built into React Native, ideal for simple user preferences or non-sensitive data.

Question 7

What is the main difference between a controlled and an uncontrolled input in React Native?

Accepted Answer

A controlled input is managed by React state via value and onChangeText props, allowing full control over the value at any time. An uncontrolled input uses a ref to directly access the DOM value without going through React state. Controlled inputs are recommended as they facilitate real-time validation and synchronization with the application state.

Question 8

What is the main role of React.memo in React Native performance optimization?

Accepted Answer

React.memo is a Higher-Order Component that memoizes the render result of a functional component. It prevents unnecessary re-renders by comparing current props with previous ones (shallow comparison by default). If props haven't changed, React reuses the memoized result instead of re-rendering the component, which significantly improves performance in lists or complex component trees.

Question 9

What is a memory leak in a React Native application?

Accepted Answer

A memory leak occurs when objects in memory are no longer used by the application but cannot be freed by the garbage collector because references to these objects still exist. In React Native, this commonly happens with uncleaned subscriptions, timers still active after unmount, or closures capturing stale references. Memory leaks gradually degrade performance and can cause crashes during long sessions.

Question 10

What is component architecture in a React Native application?

Accepted Answer

Component architecture involves structuring the application into reusable and independent elements, each with a single responsibility. This approach promotes code reuse, simplifies unit testing, and improves maintainability. Each component encapsulates its own state, logic, and presentation, enabling complex interfaces to be built from simple, composable building blocks.

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JavaScript Essentials

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