feat: add functions_deeply.js file

Author: ExploitEngineer

part3 (Fundamental Concepts)/04_functions_deeply.js

@@ -0,0 +1,71 @@
+// Function Statement (a.k.a. Function Declaration)
+a(); // Works because of hoisting
+function a() {
+  console.log("a called");
+}
+
+// Function Expression
+// Not hoisted like declarations
+let b = function () {
+  console.log("b called");
+};
+b();
+
+// Anonymous Function (function without a name)
+// Usually used in function expressions or callbacks
+let c = function () {
+  console.log("anonymous function");
+};
+c();
+
+// ❌ Not valid alone:
+// function () { console.log("error"); }; // SyntaxError
+
+// Named Function Expression
+let d = function abcd() {
+  console.log("Named function expression");
+};
+d();
+// console.log(abcd); // ❌ ReferenceError (name is not accessible outside)
+
+// First-Class Functions
+// Functions can be passed as arguments, returned from other functions, and stored in variables
+
+function sayHello() {
+  return "Hello!";
+}
+
+function executeFn(fn) {
+  console.log("Result:", fn()); // Passing function as argument
+}
+executeFn(sayHello);
+
+// Returning a function
+function outer() {
+  return function () {
+    console.log("I’m inside a returned function");
+  };
+}
+const innerFn = outer();
+innerFn(); // Outputs: I’m inside a returned function
+
+// Arrow Functions (ES6)
+// Shorter syntax, `this` is lexically scoped
+const greet = (name) => {
+  console.log(`Hello, ${name}`);
+};
+greet("Rafay");
+
+// IIFE – Immediately Invoked Function Expression
+(function () {
+  console.log("IIFE called immediately!");
+})();
+
+// Callback Functions
+function loadData(callback) {
+  console.log("Fetching data...");
+  callback(); // calling the passed function
+}
+loadData(function () {
+  console.log("Callback called after fetching.");
+});