The DOM (Document Object Model) is a tree representation of an HTML document.

JavaScript interacts with the DOM to read, modify, add, or remove elements. Methods like getElementById() and querySelector() are used for access.

DOM manipulation allows dynamic updates without reloading the page. This is a core concept in frontend interviews.

JavaScript handles events such as clicks, key presses, and form submissions.

An event listener waits for an event and then triggers a callback function. Events can bubble up or be captured down the DOM tree.

This mechanism enables interactive behavior. Understanding events is crucial for UI development.

The execution context defines how JavaScript code is evaluated and executed. It includes the variable environment, scope chain, and this keyword.

JavaScript uses a call stack to manage execution contexts. Each function call creates a new execution context. This explains how functions and scopes work internally.

let and const are preferred in modern JavaScript.

Always prefer === to avoid unexpected results.

Arrow functions are widely used today.

Both indicate absence of value but are used differently.

JavaScript is interpreted but modern engines use JIT (Just-In-Time) compilation. Code is executed line by line with optimizations.

This makes JavaScript fast and flexible. Interviewers often expect this explanation. It explains browser performance.

JavaScript has primitive types like string, number, boolean, null, undefined, symbol, and bigint. Objects are non-primitive. Dynamic typing allows variables to change types. Understanding data types avoids runtime errors. This is a basic interview topic.

Hoisting moves variable and function declarations to the top of their scope. var is hoisted but initialized as undefined. let and const are hoisted but not accessible before declaration. This explains unexpected undefined values. Hoisting questions are very common.

Scope defines where variables can be accessed. JavaScript has global, function, and block scope. let and const respect block scope. Proper scoping prevents bugs. This is essential for clean code.

Functions are reusable blocks of code. They can take parameters and return values. JavaScript supports normal, arrow, and anonymous functions. Functions are first-class citizens. This means they can be passed as arguments.

An array stores ordered collections of data. Elements are accessed by index. Arrays support methods like push, pop, map, and filter. Arrays are heavily used in frontend logic. Interviewers frequently ask this.

Objects store key-value pairs. They represent real-world entities. Properties and methods define object behavior. Objects are fundamental in JavaScript. Almost everything in JS is an object.

A callback is a function passed as an argument to another function. It executes after a task completes. Callbacks enable asynchronous programming. They are used in events and API calls. This is a core JS concept.

Asynchronous JS allows non-blocking execution. It uses callbacks, promises, and async/await. This keeps applications responsive. API calls and timers use async behavior. Interviews often test async understanding.

A promise represents a future value. It can be pending, resolved, or rejected. Promises handle async operations cleanly. They avoid callback hell. Promises are widely used in APIs.

console.log() prints values to the browser console. It is used for debugging. Developers inspect variables and logic flow. It does not affect UI. This is a simple but common interview question.

JavaScript adds interactivity to websites. It works with HTML and CSS. Frameworks like React depend on JavaScript. Modern web apps rely heavily on JS. It is essential for frontend roles.