JavaScript Control Flow

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What is Control Flow?

Control Flow in JavaScript refers to the order in which code is executed.

By default, JavaScript runs code from top to bottom, but control flow statements let you:

• Make decisions (if, else)
• Repeat code using loops
• Handle multiple outcomes (switch)
• Exit early (break, return, continue)

1. if, else if, else Statements

Syntax:

if (condition) {
    // code runs if condition is true
} else if (anotherCondition) {
    // code runs if anotherCondition is true
} else {
    // code runs if none of the above are true
}

Example:

let age = 20;

if (age >= 18) {
  console.log("You are an adult.");
} else {
  console.log("You are a minor.");
}

2. switch Statement

The switch statement is used to handle multiple conditions more cleanly than many else ifs.

Syntax:

switch (expression) {
  case value1:
    // code block
    break;
  case value2:
    // code block
    break;
  default:
    // default code block
}

Example:

let color = "blue";

switch (color) {
  case "red":
    console.log("Stop!");
    break;
  case "yellow":
    console.log("Get ready!");
    break;
  case "green":
    console.log("Go!");
    break;
  default:
    console.log("Unknown color");
}

3. Loops in JavaScript

Loops let you run a block of code repeatedly, either a set number of times or until a condition is false.

for Loop

Use when you know how many times to loop.

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

while Loop

Runs while a condition is true.

let i = 1;
while (i <= 3) {
  console.log("While loop:", i);
  i++;
}                                    

do...while Loop

Runs at least once, even if the condition is false.

let i = 1;
do {
  console.log("Do-While:", i);
  i++;
} while (i <= 3);                                                   

for...of Loop

Used to iterate over arrays or iterable objects.

let fruits = ["apple", "banana", "mango"];

for (let fruit of fruits) {
  console.log(fruit);
}                                                                             

for...in Loop

Used to iterate over object properties.

let person = { name: "Sam", age: 25 };

for (let key in person) {
    console.log(key, "=", person[key]);
}                                                                                                       

4. break,continue,return

break:

Exits the current loop or switch early.

for (let i = 1; i <= 5; i++) {
if (i === 3) break;
    console.log(i);  // Output: 1, 2
}                                                                                                                                    

continue:

Skips the current iteration and continues with the next one.

for (let i = 1; i <= 5; i++) {
if (i === 3) continue;
    console.log(i);  // Output: 1, 2, 4, 5
}                                                                                                                                                                    

return:

Ends function execution and returns a value (covered more in functions chapter).

function multiply(a, b) {
    return a * b;
}                                                                                                                                                                                                  

Summary

Control Type	Statement	Purpose
Decision	if, else	Run code conditionally
Multi-condition	switch	Cleaner alternative to many ifs
Repetition	for, while	Repeat code while condition holds
Break flow	break	Exit loop/switch early
Skip iteration	continue	Skip current loop iteration
Exit function	return	Return value from function

🧪 Practice Challenge:

Task:

Write a script that checks a number and prints:

• "Fizz" if divisible by 3
• "Buzz" if divisible by 5
• "FizzBuzz" if divisible by both
• The number itself otherwise

let num = 15;

if (num % 3 === 0 && num % 5 === 0) {
  console.log("FizzBuzz");
} else if (num % 3 === 0) {
  console.log("Fizz");
} else if (num % 5 === 0) {
  console.log("Buzz");
} else {
  console.log(num);
}