Module 05 // Core JavaScript

Function Fundamentals

Module Objective

Function declarations vs expressions, parameters, return values, recursion

Mental Model Realtime Simulation

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Practical Code Examples

// Example 1
// 1. Declarations are Hoisted
console.log(sayHi()); // "Hi!" ✅ Works

function sayHi() {
  return "Hi!";
}

// Expressions are NOT hoisted
// console.log(sum(1, 2)); // ❌ ReferenceError
const sum = (a, b) => a + b;
💡 Function declarations are moved to the top of their scope during the creation phase. Expressions are not, behaving like any other variable.
// Example 2
// 2. Default Parameters
function setRole(user, role = 'guest') {
  console.log(`User ${user} is a ${role}`);
}

setRole("Subhajit", "admin"); // "Subhajit is a admin"
setRole("Alex");              // "Alex is a guest"
💡 Default parameters allow you to initialize functions with values if no argument or `undefined` is passed.
// Example 3
// 3. Recursion
function factorial(n) {
  if (n === 1) return 1; // Base case
  return n * factorial(n - 1);
}

console.log(factorial(5)); // 120
💡 A function can call itself. This is called recursion. You must always have a **base case** to prevent an infinite loop (Stack Overflow).

Engine & Memory Architecture

Functions in Memory

1. Allocation:

  • Function code is stored in the Heap as a complex object.
  • The function name holds a pointer to that object.

2. Execution (The Call Stack):

  • Every time a function is invoked, a new Execution Context (Stack Frame) is pushed onto the Stack.
  • This frame holds the function's arguments and local variables.
  • When the function returns, the frame is popped off, and memory for local variables is freed.

3. Stack Overflow:

  • If too many functions are called (e.g., deep recursion without a base case), the Stack runs out of memory, causing a "Maximum call stack size exceeded" error.
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