The main difference between var , let and const are :

var: Declares variables with function or global scope and allows re-declaration and updates within the same scope.

let: Declares variables with block scope, allowing updates but not re-declaration within the same block.

const: Declares block-scoped variables that cannot be reassigned after their initial assignment.

The main difference between map , forEach and filter are :

map(): Creates a new array with the results of calling a provided function on every element in the array.

forEach(): Executes a provided function once for each array element.

filter(): Creates a new array with all elements that pass the test implemented by the provided function.

Regular functions and arrow functions are two common ways to define functions in JavaScript, each with distinct behaviors. Regular functions offer traditional syntax and this context handling, while arrow functions provide a concise syntax and lexical this binding, making them ideal for callbacks and simpler expressions.

JavaScript Promises make handling asynchronous operations like API calls, file loading, or time delays easier. Think of a Promise as a placeholder for a value that will be available in the future. It can be in one of three states

Pending: The task is in the initial state.

Fulfilled: The task was completed successfully, and the result is available.

Rejected: The task failed, and an error is provided.

A closure is a function that allows access to variables from its outer function and global variables, even after the outer function has finished executing. This enables functions to “remember” their environment.