JavaScript Control Flow

Control flow statements determine the order in which your code executes. They allow you to make decisions, repeat actions, and handle different scenarios in your programs.

🎛️ Control Flow Categories

Conditional

Make decisions in code

if, else, switch, ternary

Loops

Repeat actions

for, while, do-while

Jump

Control loop execution

break, continue, return

Error Handling

Manage exceptions

try, catch, finally, throw

Other

Additional control

label, with

🎯 If-Else Statements

Conditional Execution

If-else statements allow your program to make decisions and execute different code blocks based on conditions.

Statement	Syntax	Use Case
`if`	`if (condition) {...}`	Single condition
`if-else`	`if (condition) {...} else {...}`	Two alternatives
`if-else if-else`	`if (c1) {...} else if (c2) {...} else {...}`	Multiple conditions
`nested if`	`if (c1) { if (c2) {...} }`	Complex conditions

💡 Best Practices

Use descriptive condition names
Avoid deeply nested if statements
Use early returns when possible
Consider switch for multiple discrete values

🎯 Common Patterns

Validation - Check input before processing
Access Control - Check permissions
Error Handling - Check for errors
Feature Flags - Enable/disable features

Try If-Else Statements:

JavaScript Editor

// If-Else Statements - Conditional Execution

let temperature = 25;
let time = 14; // 2 PM
let isRaining = false;
let score = 85;

console.log("Initial conditions:");
console.log("Temperature:", temperature + "°C");
console.log("Time:", time + ":00");
console.log("Is raining:", isRaining);
console.log("Score:", score);

console.log("\n--- Basic If Statements ---");

// Simple if statement
if (temperature > 30) {
  console.log("It's hot outside! 🥵");
}

// If-else statement
if (temperature > 25) {
  console.log("Wear light clothes 👕");
} else {
  console.log("Wear normal clothes 🧥");
}

// If-else if-else chain
if (temperature > 30) {
  console.log("Weather: Hot");
} else if (temperature > 20) {
  console.log("Weather: Warm");
} else if (temperature > 10) {
  console.log("Weather: Cool");
} else {
  console.log("Weather: Cold");
}

console.log("\n--- Complex Conditions ---");

// Multiple conditions with logical operators
if (temperature > 20 && !isRaining) {
  console.log("Perfect weather for a walk! 🚶‍♂️");
} else {
  console.log("Better stay indoors 🏠");
}

// Nested if statements
if (time >= 6 && time < 12) {
  console.log("Good morning! ☀️");
  if (isRaining) {
    console.log("Don't forget your umbrella! ☔");
  }
} else if (time >= 12 && time < 18) {
  console.log("Good afternoon! 🌤️");
} else {
  console.log("Good evening! 🌙");
  if (temperature < 15) {
    console.log("It's getting cold, take a jacket!");
  }
}

console.log("\n--- Grade Evaluation ---");

// Practical example: Grade evaluation
if (score >= 90) {
  console.log("Grade: A 🎉");
  console.log("Excellent work!");
} else if (score >= 80) {
  console.log("Grade: B 👍");
  console.log("Good job!");
} else if (score >= 70) {
  console.log("Grade: C ✅");
  console.log("You passed!");
} else if (score >= 60) {
  console.log("Grade: D ⚠️");
  console.log("You need improvement.");
} else {
  console.log("Grade: F ❌");
  console.log("Please try again.");
}

// Conditional with function calls
function canDrive(age, hasLicense) {
  if (age >= 18 && hasLicense) {
    return "You can drive! 🚗";
  } else if (age >= 18 && !hasLicense) {
    return "You need a license! 📝";
  } else {
    return "You're too young to drive! 🚫";
  }
}

console.log("\n--- Driving Test ---");
console.log("Age 20, has license:", canDrive(20, true));
console.log("Age 20, no license:", canDrive(20, false));
console.log("Age 16, has license:", canDrive(16, true));

🔀 Switch Statements

Multiple Choice Conditions

Switch statements provide a cleaner way to handle multiple discrete values compared to long if-else if chains.

Keyword	Purpose	Important
`switch`	Start switch statement	Evaluates expression once
`case`	Define possible values	Uses strict comparison (===)
`break`	Exit switch block	⚠️ Without break, execution "falls through"
`default`	Handle all other cases	Optional but recommended

⚠️ Don't Forget Break!

Forgetting break statements causes "fall-through" behavior where multiple cases execute. This is rarely intentional.

🎯 When to Use Switch

Multiple discrete values - Days, months, roles
Simple equality checks - No complex conditions
Readability - Cleaner than long if-else chains
Intentional fall-through - Grouping cases

JavaScript Editor

// Switch Statements - Multiple Choice Conditions

let day = "Monday";
let month = 3;
let userRole = "admin";
let trafficLight = "green";

console.log("--- Day of Week ---");

// Basic switch statement
switch (day) {
  case "Monday":
    console.log("Start of the work week 💼");
    break;
  case "Tuesday":
    console.log("Second day of work");
    break;
  case "Wednesday":
    console.log("Hump day! 🐪");
    break;
  case "Thursday":
    console.log("Almost Friday!");
    break;
  case "Friday":
    console.log("Weekend is coming! 🎉");
    break;
  case "Saturday":
  case "Sunday":
    console.log("Weekend! 🏖️");
    break;
  default:
    console.log("Invalid day");
}

console.log("\n--- Month Seasons ---");

// Switch with expressions
switch (month) {
  case 12:
  case 1:
  case 2:
    console.log("Season: Winter ❄️");
    break;
  case 3:
  case 4:
  case 5:
    console.log("Season: Spring 🌸");
    break;
  case 6:
  case 7:
  case 8:
    console.log("Season: Summer ☀️");
    break;
  case 9:
  case 10:
  case 11:
    console.log("Season: Autumn 🍂");
    break;
  default:
    console.log("Invalid month");
}

console.log("\n--- User Permissions ---");

// Practical user role example
switch (userRole) {
  case "admin":
    console.log("Full access granted 🔓");
    console.log("Can manage users, content, and settings");
    break;
  case "editor":
    console.log("Content management access 📝");
    console.log("Can create and edit content");
    break;
  case "user":
    console.log("Standard user access 👤");
    console.log("Can view content and comment");
    break;
  case "guest":
    console.log("Limited access 🔒");
    console.log("Can only view public content");
    break;
  default:
    console.log("Unknown role, please contact support");
}

console.log("\n--- Traffic Light System ---");

// Traffic light simulation
switch (trafficLight) {
  case "red":
    console.log("🛑 STOP!");
    console.log("Wait for green light");
    break;
  case "yellow":
    console.log("⚠️ CAUTION!");
    console.log("Prepare to stop");
    break;
  case "green":
    console.log("✅ GO!");
    console.log("Proceed with caution");
    break;
  default:
    console.log("🚨 MALFUNCTION!");
    console.log("Treat as four-way stop");
}

console.log("\n--- Calculator with Switch ---");

// Simple calculator using switch
function calculate(a, b, operation) {
  let result;
  switch (operation) {
    case "+":
      result = a + b;
      break;
    case "-":
      result = a - b;
      break;
    case "*":
      result = a * b;
      break;
    case "/":
      result = b !== 0 ? a / b : "Error: Division by zero";
      break;
    case "%":
      result = a % b;
      break;
    case "**":
      result = a ** b;
      break;
    default:
      result = "Invalid operation";
  }
  return result;
}

console.log("5 + 3 =", calculate(5, 3, "+"));
console.log("10 - 4 =", calculate(10, 4, "-"));
console.log("6 * 7 =", calculate(6, 7, "*"));
console.log("15 / 3 =", calculate(15, 3, "/"));
console.log("8 / 0 =", calculate(8, 0, "/"));

🔄 For Loops

Controlled Iteration

For loops are ideal when you know exactly how many times you want to iterate. They provide precise control over the loop counter.

Part	Purpose	Example
Initialization	Set loop counter	`let i = 0`
Condition	Check before each iteration	`i < 10`
Increment	Update counter after each iteration	`i++`

💡 For Loop Variations

for...in - Iterate over object properties
for...of - Iterate over iterable values (ES6)
forEach() - Array method for iteration
for await...of - Async iteration (ES2018)

🎯 Common Use Cases

Array processing - Transform, filter, search
Number sequences - Count, generate patterns
DOM manipulation - Process multiple elements
Data processing - Calculate sums, averages

JavaScript Editor

// For Loops - Controlled Iteration

console.log("--- Basic For Loop ---");

// Count from 1 to 5
for (let i = 1; i <= 5; i++) {
  console.log("Count:", i);
}

console.log("\n--- Countdown ---");

// Countdown from 10 to 1
for (let i = 10; i >= 1; i--) {
  console.log("T-minus", i + "...");
}
console.log("🚀 Blast off!");

console.log("\n--- Even Numbers ---");

// Even numbers from 2 to 10
for (let i = 2; i <= 10; i += 2) {
  console.log("Even number:", i);
}

console.log("\n--- Multiplication Table ---");

// Multiplication table
let number = 7;
console.log("Multiplication table for", number + ":");
for (let i = 1; i <= 10; i++) {
  console.log(number + " × " + i + " = " + (number * i));
}

console.log("\n--- Array Iteration ---");

// Iterating through arrays
let fruits = ["apple", "banana", "orange", "grape", "mango"];
console.log("Fruits array:", fruits);

console.log("\nFruits list:");
for (let i = 0; i < fruits.length; i++) {
  console.log((i + 1) + ". " + fruits[i]);
}

console.log("\n--- Sum Calculation ---");

// Calculate sum of numbers
let numbers = [5, 10, 15, 20, 25];
let sum = 0;

for (let i = 0; i < numbers.length; i++) {
  sum += numbers[i];
  console.log("Adding", numbers[i] + ", current sum:", sum);
}

console.log("Final sum:", sum);
console.log("Average:", sum / numbers.length);

console.log("\n--- Nested For Loops ---");

// Nested loops for patterns
console.log("Number pattern:");
for (let i = 1; i <= 3; i++) {
  let row = "";
  for (let j = 1; j <= 3; j++) {
    row += "(" + i + "," + j + ") ";
  }
  console.log(row);
}

console.log("\n--- Break and Continue ---");

// Using break and continue
console.log("Numbers from 1 to 10 (skip 5, stop at 8):");
for (let i = 1; i <= 10; i++) {
  if (i === 5) {
    continue; // Skip 5
  }
  if (i === 9) {
    break; // Stop at 9
  }
  console.log(i);
}

console.log("\n--- Loop with Condition ---");

// Finding specific elements
let scores = [85, 92, 78, 95, 88, 76];
let passingScore = 80;

console.log("Scores:", scores);
console.log("Passing scores (>= " + passingScore + "):");

for (let i = 0; i < scores.length; i++) {
  if (scores[i] >= passingScore) {
    console.log("Score at index", i + ":", scores[i]);
  }
}

⏳ While & Do-While Loops

Conditional Iteration

While loops are used when you don't know how many times you need to iterate in advance, but you know the condition to stop.

Loop Type	Syntax	When to Use
`while`	`while (condition) {...}`	Check condition before iteration
`do-while`	`do {...} while (condition);`	Check condition after iteration

Key Differences:

while - May execute 0 times
do-while - Always executes at least once

⚠️ Infinite Loop Danger

Always ensure the loop condition eventually becomes false. Infinite loops can crash your program or browser.

🎯 Common Use Cases

User input - Wait for valid input
Game loops - Continue until game over
Data streams - Process until end
Retry logic - Retry until success or limit

🔧 Loop Control

Use break to exit early and continue to skip to next iteration. Always have an escape condition!

JavaScript Editor

// While and Do-While Loops - Conditional Iteration

console.log("--- While Loop ---");

// Basic while loop
let count = 1;
while (count <= 5) {
  console.log("While loop count:", count);
  count++;
}

console.log("\n--- Countdown with While ---");

// Countdown with while
let timer = 5;
while (timer > 0) {
  console.log("Time left:", timer + " seconds");
  timer--;
}
console.log("⏰ Time's up!");

console.log("\n--- User Input Simulation ---");

// Simulating user input validation
let userInput = "";
let attempts = 0;
const correctPassword = "secret123";

// This simulates multiple login attempts
while (userInput !== correctPassword && attempts < 3) {
  attempts++;
  // Simulating different password attempts
  if (attempts === 1) userInput = "wrongpass";
  else if (attempts === 2) userInput = "anotherwrong";
  else userInput = "secret123";
  
  console.log("Attempt", attempts + ":", userInput === correctPassword ? "✅ Access granted!" : "❌ Wrong password");
}

console.log("\n--- Do-While Loop ---");

// Do-while loop (executes at least once)
let number;
do {
  // Simulating random number generation
  number = Math.floor(Math.random() * 10) + 1;
  console.log("Generated number:", number);
} while (number !== 7);

console.log("🎯 Finally got a 7!");

console.log("\n--- Menu System ---");

// Simple menu system simulation
let choice = 0;
let totalAmount = 0;

console.log("🛒 Shopping Cart Simulation");
do {
  // Simulating menu choices
  if (choice === 0) choice = 1;
  else if (choice === 1) choice = 2;
  else if (choice === 2) choice = 3;
  else choice = 0;
  
  switch (choice) {
    case 1:
      console.log("Added: Apple - $1.50");
      totalAmount += 1.5;
      break;
    case 2:
      console.log("Added: Banana - $0.75");
      totalAmount += 0.75;
      break;
    case 3:
      console.log("Added: Orange - $1.25");
      totalAmount += 1.25;
      break;
    case 0:
      console.log("🛒 Checkout completed!");
      break;
  }
} while (choice !== 0);

console.log("Total amount: $" + totalAmount.toFixed(2));

console.log("\n--- Number Guessing Game ---");

// Number guessing game simulation
let targetNumber = 42;
let guess = 0;
let attempts2 = 0;
const maxAttempts = 5;

console.log("🎮 Guess the number (1-100)");
console.log("Target number is:", targetNumber); // Normally hidden

while (guess !== targetNumber && attempts2 < maxAttempts) {
  attempts2++;
  // Simulating different guesses
  if (attempts2 === 1) guess = 25;
  else if (attempts2 === 2) guess = 50;
  else if (attempts2 === 3) guess = 40;
  else if (attempts2 === 4) guess = 45;
  else guess = 42;
  
  if (guess < targetNumber) {
    console.log("Attempt", attempts2 + ": " + guess + " - Too low! 📉");
  } else if (guess > targetNumber) {
    console.log("Attempt", attempts2 + ": " + guess + " - Too high! 📈");
  } else {
    console.log("Attempt", attempts2 + ": " + guess + " - 🎉 Correct! You win!");
  }
}

if (guess !== targetNumber) {
  console.log("💔 Game over! The number was", targetNumber);
}

⏭️ Break & Continue

Loop Control Statements

Break and continue give you fine-grained control over loop execution, allowing you to exit early or skip iterations.

Statement	Effect	Use Case
`break`	Exit the entire loop immediately	Found what you're looking for
`continue`	Skip to next iteration	Skip invalid or unwanted items
`break label`	Exit labeled statement	Exit nested loops
`continue label`	Continue labeled loop	Skip to next iteration of outer loop

💡 Performance Tips

Use break early when target is found
Use continue to skip unnecessary processing
Avoid complex nested loops when possible
Consider array methods for simple iterations

🎯 Practical Examples

Search - Break when item found
Validation - Continue if invalid
Filtering - Skip unwanted elements
Optimization - Stop when condition met

JavaScript Editor

// Break and Continue - Loop Control

console.log("--- Break Statement ---");

// Break stops the entire loop
console.log("Searching for number 5 in array:");
let numbers = [1, 3, 7, 5, 9, 2, 4];

for (let i = 0; i < numbers.length; i++) {
  console.log("Checking:", numbers[i]);
  if (numbers[i] === 5) {
    console.log("✅ Found number 5 at index", i);
    break; // Exit loop immediately
  }
}

console.log("\n--- Continue Statement ---");

// Continue skips to next iteration
console.log("Printing odd numbers from 1 to 10:");
for (let i = 1; i <= 10; i++) {
  if (i % 2 === 0) {
    continue; // Skip even numbers
  }
  console.log("Odd number:", i);
}

console.log("\n--- Practical Example: Data Processing ---");

// Process user data, skip invalid entries
let users = [
  { name: "Alice", age: 25, active: true },
  { name: "Bob", age: 17, active: true },
  { name: "Charlie", age: 0, active: true }, // Invalid age
  { name: "", age: 30, active: true }, // Invalid name
  { name: "Eve", age: 22, active: false }, // Inactive user
  { name: "Frank", age: 28, active: true }
];

console.log("Valid active users (18+ with valid names):");

for (let i = 0; i < users.length; i++) {
  let user = users[i];
  
  // Skip inactive users
  if (!user.active) {
    console.log("Skipping", user.name || "unnamed user", "- inactive");
    continue;
  }
  
  // Skip users with invalid names
  if (!user.name || user.name.trim() === "") {
    console.log("Skipping user at index", i, "- invalid name");
    continue;
  }
  
  // Skip underage users
  if (user.age < 18 || user.age > 120) {
    console.log("Skipping", user.name, "- invalid age:", user.age);
    continue;
  }
  
  console.log("✅ Valid user:", user.name + ", age", user.age);
}

console.log("\n--- Break in While Loop ---");

// Break in while loop - number search
let data = [10, 20, 30, 40, 50, 60, 70];
let searchValue = 40;
let index = 0;
let found = false;

while (index < data.length) {
  console.log("Searching at index", index + ":", data[index]);
  
  if (data[index] === searchValue) {
    console.log("🎯 Found", searchValue, "at index", index);
    found = true;
    break;
  }
  
  index++;
}

if (!found) {
  console.log("❌", searchValue, "not found in array");
}

console.log("\n--- Nested Loops with Break ---");

// Break with labels (rarely used but powerful)
console.log("Searching for pair that sums to 10:");
let nums = [2, 4, 6, 8, 3, 7];

outerLoop: // Label for the outer loop
for (let i = 0; i < nums.length; i++) {
  for (let j = i + 1; j < nums.length; j++) {
    if (nums[i] + nums[j] === 10) {
      console.log("Found:", nums[i] + " + " + nums[j] + " = 10");
      console.log("Stopping search...");
      break outerLoop; // Break out of both loops
    }
    console.log("Checking:", nums[i] + " + " + nums[j] + " = " + (nums[i] + nums[j]));
  }
}

console.log("\n--- Continue with Nested Loops ---");

// Continue with nested loops
console.log("Multiplication table (skip 5s):");
for (let i = 1; i <= 3; i++) {
  if (i === 2) continue; // Skip the 2 times table
  
  for (let j = 1; j <= 3; j++) {
    if (i * j === 6) continue; // Skip 6
    console.log(i + " × " + j + " = " + (i * j));
  }
}

🚨 Error Handling

Try-Catch-Finally

Error handling allows your program to gracefully handle unexpected situations without crashing. It's essential for robust applications.

Block	Purpose	When Executes
`try`	Code that might throw errors	Always, until error occurs
`catch`	Handle thrown errors	Only if error occurs in try
`finally`	Cleanup code	Always, regardless of errors
`throw`	Create custom errors	When you want to signal an error

⚠️ Error Handling Best Practices

Only catch errors you can handle
Always log errors for debugging
Use specific error types when possible
Don't swallow errors silently
Use finally for cleanup (file close, etc.)

🎯 Common Error Types

Error - Generic error
TypeError - Wrong type
RangeError - Out of range
ReferenceError - Undefined variable
SyntaxError - Code syntax issues

JavaScript Editor

// Error Handling with Try-Catch

console.log("--- Basic Try-Catch ---");

// Basic error handling
try {
  console.log("Starting operation...");
  let result = 10 / 2;
  console.log("Division result:", result);
  
  // This will cause an error
  let invalidResult = 10 / 0;
  console.log("This won't be printed");
} catch (error) {
  console.log("❌ An error occurred:", error.message);
} finally {
  console.log("✅ This always executes");
}

console.log("\n--- Handling Specific Errors ---");

// Handling different types of errors
function processData(data) {
  try {
    if (!data) {
      throw new Error("No data provided");
    }
    
    if (typeof data !== 'number') {
      throw new TypeError("Data must be a number");
    }
    
    if (data < 0) {
      throw new RangeError("Data must be positive");
    }
    
    console.log("Data processed successfully:", data);
    
  } catch (error) {
    if (error instanceof TypeError) {
      console.log("Type error:", error.message);
    } else if (error instanceof RangeError) {
      console.log("Range error:", error.message);
    } else {
      console.log("General error:", error.message);
    }
  }
}

processData(42);      // Success
processData();        // No data
processData("hello"); // Wrong type
processData(-5);      // Negative number

console.log("\n--- JSON Parsing with Error Handling ---");

// Safe JSON parsing
function safeJSONParse(jsonString) {
  try {
    let data = JSON.parse(jsonString);
    console.log("✅ Valid JSON:", data);
    return data;
  } catch (error) {
    console.log("❌ Invalid JSON:", error.message);
    return null;
  }
}

let validJSON = '{"name": "John", "age": 30}';
let invalidJSON = '{"name": "John", "age": 30';

safeJSONParse(validJSON);
safeJSONParse(invalidJSON);

console.log("\n--- Division with Error Handling ---");

// Robust division function
function safeDivide(a, b) {
  try {
    if (b === 0) {
      throw new Error("Division by zero is not allowed");
    }
    
    if (typeof a !== 'number' || typeof b !== 'number') {
      throw new TypeError("Both arguments must be numbers");
    }
    
    return a / b;
    
  } catch (error) {
    console.log("Division error:", error.message);
    return null;
  } finally {
    console.log("Division operation completed");
  }
}

console.log("10 / 2 =", safeDivide(10, 2));
console.log("10 / 0 =", safeDivide(10, 0));
console.log("10 / 'hello' =", safeDivide(10, 'hello'));

console.log("\n--- Custom Error Classes ---");

// Custom error types
class ValidationError extends Error {
  constructor(field, message) {
    super(message);
    this.field = field;
    this.name = "ValidationError";
  }
}

class DatabaseError extends Error {
  constructor(operation, message) {
    super(message);
    this.operation = operation;
    this.name = "DatabaseError";
  }
}

// Using custom errors
function validateUser(user) {
  try {
    if (!user.name) {
      throw new ValidationError("name", "Name is required");
    }
    
    if (user.age < 0 || user.age > 150) {
      throw new ValidationError("age", "Age must be between 0 and 150");
    }
    
    console.log("✅ User validation passed");
    
  } catch (error) {
    if (error instanceof ValidationError) {
      console.log("Validation failed for", error.field + ":", error.message);
    } else {
      console.log("Unexpected error:", error.message);
    }
  }
}

validateUser({ name: "John", age: 25 });
validateUser({ name: "", age: 25 });
validateUser({ name: "Jane", age: -5 });

🎮 Practice: User Management System

Build a complete user management system that uses all the control flow concepts you've learned. This includes validation, loops, error handling, and conditional logic.

JavaScript Editor

// Practice: Build a Complete User Management System

class UserManager {
  constructor() {
    this.users = [];
    this.nextId = 1;
  }

// Add user with validation
  addUser(name, age, email) {
    try {
      // Validation checks
      if (!name || name.trim() === "") {
        throw new Error("Name is required");
      }
      
      if (typeof age !== 'number' || age < 0 || age > 150) {
        throw new Error("Age must be a number between 0 and 150");
      }
      
      if (!email || !email.includes('@')) {
        throw new Error("Valid email is required");
      }
      
      // Check for duplicate email
      for (let user of this.users) {
        if (user.email === email) {
          throw new Error("Email already exists");
        }
      }
      
      // Add user
      const newUser = {
        id: this.nextId++,
        name: name.trim(),
        age: age,
        email: email,
        active: true
      };
      
      this.users.push(newUser);
      console.log("✅ User added:", newUser.name);
      return newUser;
      
    } catch (error) {
      console.log("❌ Failed to add user:", error.message);
      return null;
    }
  }

// Find user by ID
  findUserById(id) {
    for (let user of this.users) {
      if (user.id === id) {
        return user;
      }
    }
    return null;
  }

// Get active users
  getActiveUsers() {
    const activeUsers = [];
    for (let user of this.users) {
      if (user.active) {
        activeUsers.push(user);
      }
    }
    return activeUsers;
  }

// Deactivate user
  deactivateUser(id) {
    const user = this.findUserById(id);
    if (user) {
      user.active = false;
      console.log("✅ User deactivated:", user.name);
      return true;
    }
    console.log("❌ User not found with ID:", id);
    return false;
  }

// Display all users
  displayUsers() {
    console.log("\n=== ALL USERS ===");
    if (this.users.length === 0) {
      console.log("No users found");
      return;
    }
    
    for (let i = 0; i < this.users.length; i++) {
      const user = this.users[i];
      const status = user.active ? "🟢 Active" : "🔴 Inactive";
      console.log(`${i + 1}. ${user.name} (ID: ${user.id}) - ${status}`);
      console.log(`   Age: ${user.age}, Email: ${user.email}`);
    }
  }

// Get user statistics
  getUserStats() {
    let activeCount = 0;
    let totalAge = 0;
    let ageGroups = { young: 0, adult: 0, senior: 0 };

for (let user of this.users) {
      if (user.active) {
        activeCount++;
        totalAge += user.age;
        
        // Categorize by age
        if (user.age < 18) ageGroups.young++;
        else if (user.age < 65) ageGroups.adult++;
        else ageGroups.senior++;
      }
    }

const averageAge = activeCount > 0 ? totalAge / activeCount : 0;

return {
      totalUsers: this.users.length,
      activeUsers: activeCount,
      averageAge: averageAge.toFixed(1),
      ageGroups: ageGroups
    };
  }
}

// Test the User Management System
console.log("🧪 TESTING USER MANAGEMENT SYSTEM\n");

const userManager = new UserManager();

// Add users (some valid, some invalid)
console.log("--- Adding Users ---");
userManager.addUser("Alice Johnson", 25, "alice@email.com");
userManager.addUser("Bob Smith", 30, "bob@email.com");
userManager.addUser("", 25, "invalid@email.com"); // Invalid name
userManager.addUser("Charlie Brown", -5, "charlie@email.com"); // Invalid age
userManager.addUser("Diana Prince", 28, "diana@email.com");
userManager.addUser("Alice Johnson", 25, "alice@email.com"); // Duplicate email

console.log("\n--- Displaying Users ---");
userManager.displayUsers();

console.log("\n--- User Statistics ---");
const stats = userManager.getUserStats();
console.log("Total users:", stats.totalUsers);
console.log("Active users:", stats.activeUsers);
console.log("Average age:", stats.averageAge);
console.log("Age groups:", stats.ageGroups);

console.log("\n--- Managing User Status ---");
userManager.deactivateUser(2); // Deactivate Bob
userManager.deactivateUser(99); // Try to deactivate non-existent user

console.log("\n--- Active Users Only ---");
const activeUsers = userManager.getActiveUsers();
console.log("Active users count:", activeUsers.length);
for (let user of activeUsers) {
  console.log(`- ${user.name} (${user.email})`);
}

console.log("\n--- Final User List ---");
userManager.displayUsers();

// Additional Challenge: Search functionality
console.log("\n--- Search Challenge ---");
function searchUsers(users, query) {
  const results = [];
  query = query.toLowerCase();
  
  for (let user of users) {
    if (user.name.toLowerCase().includes(query) || 
        user.email.toLowerCase().includes(query)) {
      results.push(user);
    }
  }
  
  return results;
}

const searchResults = searchUsers(userManager.users, "ali");
console.log("Search results for 'ali':", searchResults.length, "users found");

💪 Additional Challenges:

Add email validation with regex
Implement user update functionality
Add pagination for user lists

Create user search with multiple criteria
Add bulk user operations
Implement user roles and permissions

📚 Control Flow Summary

Key Takeaways:

Use if-else for conditional execution
Use switch for multiple discrete values
Choose the right loop for your iteration needs
Always handle errors gracefully

Best Practices:

Keep conditions simple and readable
Avoid deeply nested structures
Use break and continue judiciously
Always have an escape condition for loops
Handle errors at the appropriate level

Now that you can control program flow, you're ready to learn about functions - the building blocks of reusable code!

Next: Functions →

📋 Control Flow Quick Reference

Conditional:

if (condition) {...}if (c) {...} else {...}switch(value) { case: ... }

Loops:

for (let i=0; i<n; i++)while (condition) {...}

Jump:

breakcontinuereturn

Error:

try {...} catch(e) {...}throw new Error("message")

Patterns:

Early return for validation
Loop until condition met
Handle errors at boundaries
Use descriptive condition names
Avoid magic numbers in conditions

← Operators Loops →

JavaScript Tutorial

JavaScript Control Flow

🎛️ Control Flow Categories

Conditional

Loops

Jump

Error Handling

Other

🎯 If-Else Statements

Conditional Execution

💡 Best Practices

🎯 Common Patterns

Try If-Else Statements:

🔀 Switch Statements

Multiple Choice Conditions

⚠️ Don't Forget Break!

🎯 When to Use Switch

🔄 For Loops

Controlled Iteration

💡 For Loop Variations

🎯 Common Use Cases

⏳ While & Do-While Loops

Conditional Iteration

Key Differences:

⚠️ Infinite Loop Danger

🎯 Common Use Cases

🔧 Loop Control

⏭️ Break & Continue

Loop Control Statements

💡 Performance Tips

🎯 Practical Examples

🚨 Error Handling

Try-Catch-Finally

⚠️ Error Handling Best Practices

🎯 Common Error Types

🎮 Practice: User Management System

💪 Additional Challenges:

📚 Control Flow Summary

Key Takeaways:

Best Practices:

📋 Control Flow Quick Reference

Conditional:

Loops:

Jump:

Error:

Patterns:

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