Summary  
Functions in JavaScript are reusable named or anonymous blocks of code defined using declarations, expressions, or arrow syntax, complete with parameters, return values, and their own local scope.

General domain of usage  
Web development


Functions help you organize and reuse code in JavaScript. A function is a named block of code that performs a specific task. You can define a function once and call it whenever needed.

There are three common ways to create functions: **function declarations**, **function expressions**, and **arrow functions**.



## Function Declaration
A function declaration uses the function keyword followed by a name, parameters, and a block of code.

function add(a, b) {
  return a + b;
}

console.log(add(3, 4)); // 7

## Function Expression
A function expression assigns a function to a variable.

const multiply = function(a, b) {
  return a * b;
};

console.log(multiply(3, 4)); // 12

## Arrow Functions
Arrow functions provide a shorter and more modern syntax. They are widely used in React and Next.js.

const subtract = (a, b) => {
  return a - b;
};

console.log(subtract(5, 2)); // 3

For simple expressions, you can return a value without writing return:

const divide = (a, b) => a / b;

console.log(divide(10, 2)); // 5

## Function Scope
Variables declared inside a function are only available within that function. This is called **local scope**.

function greet(name) {
  const message = "Hello, " + name + "!";
  return message;
}

console.log(greet("Sam")); // Hello, Sam!

Learn the core concepts of JavaScript needed for backend development, including variables, data structures, functions, and asynchronous code. Practice working with real data and understand how JavaScript behaves outside the browser. Build a strong foundation before moving on to Node.js and server-side development.