[JavaScript] functions

🔮 What is a functions?

Functions are one of the fundamental building blocks in JavaScript. A function is a set of statements that performs a particular task of the program. This task could be just a little part of a program or even the whole program.

💡Declaring a function in JS

• The function declaration is the process of creating function, but not executing it.

function sayHi()
{
  console.log('Hello!');
}

• The process of executing(calling) the function is known as function invocation

==> as many as times as you invoke the function, that many times it will execute the code between the curly braces.
( in our case: 'Hello!');

sayHi();

💡 Function Syntax

// keyword  function   parameters (if any)
// ^         name  ________|
// |          |   |
function sayHello() {
  // the code or so called the body of the function
  // return an expression (if needed)
}

💡 Arguments and Parameters

// function declaration with a parameter
function sayHello(language) {
  switch (language) {
    case 'fr':
      console.log('Bonjour!');
      break;
    case 'ger':
      console.log('Hallo!');
      break;
    case 'esp':
      console.log('Hola!');
      break;
    default:
      console.log('Hello!');
  }
}

// function invocation with or without an argument
sayHello('ger'); // => Hallo!
sayHello('fr'); // => Bonjour!
sayHello('esp'); // => Hola!
sayHello(); // => Hello!

• Parameter is the variable between the parentheses which is part of the function declaration. In the case above: The language variable. Note that this word is a placeholder and can be any word possible.
• Argument is the value passed to the function at the moment of its invocation. In the case above: The different strings ger, fr, or esp that are passed and stored in the parameter.

// we passed argument "ger"
//                      |
//           -----------
//          |
sayHello('ger'); // => Hallo!

// we passed argument "fr"
sayHello('fr'); // => Bonjour!

// we passed argument "esp"
sayHello('esp'); // => Hola!

// we didn't pass any arguments, so the default part was executed
sayHello(); // => Hello!