1. Function Declaration and Invocation:

• Functions can be declared using the function keyword.

• Functions are executed (or invoked) by using their name followed by parentheses.

  function greet(name) {
      console.log("Hello, " + name + "!");
  }
  greet("Vignesh");    // Hello, Vignesh!
  

2. Function Parameters and Arguments:

• Parameters: Variables listed in a function's declaration. They act as placeholders for values.

• Arguments: Values passed to a function when it is invoked.

• Functions can return a value using the return keyword. If no return statement is present, the function returns undefined.

  function add(x, y) {
      return x + y;
  }
  let sum = add(5, 4); 
  console.log(sum);    //  9
  

Arrow Functions:

• Syntax
• Example:

Closure

A closure is formed when a function is defined within another function.

function outerFunction() {
    let outerVariable = 'I am from the outer function';
 
    function innerFunction() {
      console.log(outerVariable);
    }
  
    return innerFunction;
}
let closureExample = outerFunction();
closureExample(); // I am from the outer function

Different ways of creating functions in JavaScript

1. Function Declaration

A standard way to define a named function.

function greet(name) {
    return `Hello, ${name}!`;
}
console.log(greet("Dev Duo")); // Output: Hello, Dev Duo!

• Hoisted: Can be called before its declaration in the code.

2. Function Expression