JavaScript is a scripting language used to make web pages interactive and dynamic.

JavaScript is used to add interactivity such as button clicks, form validation, dynamic content updates, animations, and API handling.

Yes. JavaScript is a high-level, interpreted programming language widely used in web development.

Java and JavaScript are different languages. Java is mainly used for application development, while JavaScript is mainly used for web interactivity.

Variables can be declared using var, let, and const.

var is function-scoped, let is block-scoped, and const is block-scoped but cannot be reassigned.

Common data types are string, number, boolean, undefined, null, object, and bigint.

undefined means a variable is declared but not assigned a value. null means an intentional empty value.

Operators are symbols used to perform operations, such as arithmetic, comparison, logical, and assignment operations.

A function is a reusable block of code used to perform a specific task.

== checks value only after type conversion. === checks both value and data type without type conversion.

Arrays are used to store multiple values in a single variable.

Objects store data in key-value pairs and are used to represent real-world entities.

A function declaration is defined with a function name directly. A function expression stores a function inside a variable.

An arrow function is a shorter syntax for writing functions using =>.

Scope defines where a variable can be accessed. Common scopes are global scope, function scope, and block scope.

Hoisting is JavaScript’s behavior of moving declarations to the top of their scope before code execution.

An event is an action that happens in the browser, such as click, input, submit, mouseover, or keypress.

DOM stands for Document Object Model. It represents the HTML document as objects so JavaScript can access and modify webpage content.

Elements can be selected using methods like getElementById, getElementsByClassName, querySelector, and querySelectorAll.

Synchronous code runs line by line. Asynchronous code allows some tasks like API calls or timers to run without blocking the rest of the code.

A callback function is a function passed as an argument to another function and executed later.

A promise is an object that represents the result of an asynchronous operation. It can be pending, fulfilled, or rejected.

async and await are used to handle asynchronous operations in a cleaner and easier way than callbacks or plain promises.

A closure is a function that remembers variables from its outer scope even after the outer function has finished execution.

• map() creates a new array by transforming each item.
• filter() creates a new array with matching items.
• reduce() returns a single value by processing all items.

Destructuring is a way to extract values from arrays or objects into separate variables.

The spread operator ... is used to expand arrays, objects, or function arguments.

The rest operator ... collects multiple values into a single array or object.

Event bubbling means an event starts from the target element and then moves upward through parent elements.

Event delegation is a technique where a parent element handles events for its child elements using event bubbling.

localStorage stores data without expiry, while sessionStorage stores data only until the browser tab is closed.

A shallow copy copies only the first level. A deep copy copies all nested levels independently.

this refers to the object that is currently executing the function, depending on how the function is called.

• call() invokes a function immediately with arguments listed one by one.
• apply() invokes a function immediately with arguments passed as an array.
• bind() returns a new function with fixed this value.

Debouncing limits how often a function runs by waiting for a pause before executing it, useful in search inputs or resize events.

Throttling limits a function to run at fixed intervals, useful for scroll or resize performance optimization.

Errors can be handled using try, catch, finally, and proper promise error handling with .catch().

forEach() is used to loop through items without returning a new array. map() returns a new transformed array.

I reduce unnecessary DOM operations, use debouncing or throttling, optimize loops, reuse code, minimize global variables, and write efficient logic.

Yes, JavaScript is single-threaded, but it can handle asynchronous tasks using the event loop, callbacks, promises, and browser APIs.

Yes. A const object reference cannot be reassigned, but its properties can still be modified.

Yes, because == does type conversion. This is why === is usually safer.

No. It waits for the specified delay and then runs only when the call stack is clear.

No. In JavaScript, NaN === NaN is false.