Functions are fundamental building blocks in JavaScript. They are reusable blocks of code that perform a specific task.

Declaring a Function (Function Declaration): Uses the function keyword, followed by the function name, parentheses () for parameters, and curly braces {} for the function body.

function greet() {
  console.log("Hello there!");
}

Calling a Function: To execute a function, you "call" or "invoke" it by its name followed by parentheses.

greet(); // Output: Hello there!

Function Parameters and Arguments:

• Parameters: Variables listed in the function definition (inside the parentheses). They act as placeholders for values that will be passed to the function.
• Arguments: The actual values passed to the function when it is called.

function sayHelloTo(name) { // 'name' is a parameter
  console.log("Hello, " + name + "!");
}

sayHelloTo("Alice"); // "Alice" is an argument. Output: Hello, Alice!
sayHelloTo("Bob");   // "Bob" is an argument. Output: Hello, Bob!

The return Statement: Functions can return a value back to the caller using the return statement. If a function doesn't have a return statement, or has a return statement without a value, it implicitly returns undefined.

function add(num1, num2) {
  return num1 + num2; // Returns the sum
}

let sum = add(5, 3);
console.log(sum); // Output: 8

function doNothing() {
  // No return statement
}
let result = doNothing();
console.log(result); // Output: undefined

Once a return statement is executed, the function immediately stops executing.