JavaScript Interview Questions

JavaScript is a high-level, interpreted scripting language primarily used to create dynamic and interactive web content within browsers.

Unlike compiled languages like C++ or Java, JavaScript runs directly in the browser without compilation.

It supports multiple paradigms including object-oriented, functional, and event-driven programming.

With Node.js, JavaScript can now be executed on the server side, making it a full-stack language.

Its non-blocking I/O model and asynchronous capabilities make it ideal for modern web applications requiring real-time updates and interactivity.

var is function-scoped, meaning it's only accessible within the function it's declared in. It's also subject to hoisting and allows redeclaration.

let and const are block-scoped (e.g., inside if blocks, loops), which provides better control over variable visibility.

let allows reassignment, whereas const prevents reassigning the variable binding but not mutation of objects or arrays it references.

Best practice: Use const by default, and switch to let only when reassignment is necessary.

Understanding these scoping rules helps avoid bugs related to unintended variable access and makes code more predictable and maintainable.

A closure is a function that has access to its outer (enclosing) function’s scope, even after the outer function has finished execution.

This happens because functions in JavaScript preserve references to variables they use, even if those variables go out of scope.

Closures are widely used in module patterns, private variables, callbacks, and event handlers.

Example: A counter function that retains its count value across multiple calls due to a closure preserving the outer scope.

They enable powerful patterns such as data encapsulation and factory functions while maintaining cleaner, modular code structures.