Full Stack Development - js Functions - class 8

 Js functions are a section of reusable code. Declare it once and use it wherever you want. Call the function to execute that code.

function happyBirthday(){

    console.log("Happy birthday to you!");

    console.log("Happy birthday to you!");

  console.log(`Happy birthday dear ${username}!`);

   console.log("Happy birthday to you!");

   console.log(`You are ${age} years old!`);

}

function checkValidEmail(email)

{

   return email.includes("@") ;

}

happyBirthday();

console.log(checkValidEmail("fakeemail@fakesite.com"));

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

https://www.w3schools.com/js/js_functions.asp

1. Assigned to a variable (Function Expression)

You can store an anonymous function in a variable, which then acts as the function's identifier for calling it later. 

const greet = function() { console.log("Hello!"); }; greet(); // Output: Hello!

let x = 10;

let y = 20;

let z = (x,y)=> {return x + y;}

console.log(z(2,3));

2. As an argument (Callback Function)

They are commonly passed as arguments to higher-order functions like setTimeout(), map(), filter(), or event handlers. 

setTimeout(function() {

  console.log("This runs after 1 second.");

}, 1000);

3. Immediately Invoked Function Expressions (IIFEs)

An IIFE is an anonymous function that runs as soon as it is defined. This is useful for creating a local scope to prevent variables from polluting the global namespace. 

(function() {

  var message = "IIFE executed immediately.";

  console.log(message);

})(); 

// Output: IIFE executed immediately.

4. Arrow Functions

Arrow functions provide a more concise syntax for anonymous functions, especially for short, one-line operations. 

const numbers = [1, 2, 3];

const doubled = numbers.map(el => el * 2);

console.log(doubled); // Output: [2, 4, 6]