Control Flow in JavaScript: If, Else, and Switch Explained

In programming, control flow means deciding which part of the code should run depending on a condition. Just like in real life, we make decisions based on situations.

Example:

• If it rains → take an umbrella ☔

• Else → go out normally

JavaScript uses if, else, and switch statements to make these decisions.

---

1. The if Statement

4

The if statement runs code only when a condition is true.

Example

let age = 18;

if (age >= 18) {
  console.log("You can vote");
}

How it works

1. Check the condition age >= 18

2. If true → run the code inside { }

3. If false → skip the block

---

2. The if-else Statement

Sometimes we want two possible outcomes.

Example

let age = 16;

if (age >= 18) {
  console.log("You can vote");
} else {
  console.log("You cannot vote yet");
}

Flow

• Condition true → first block runs

• Condition false → else block runs

This helps programs handle both situations.

---

3. The else if Ladder

When we have multiple conditions, we use else if.

Example

let marks = 75;

if (marks >= 90) {
  console.log("Grade A");
} else if (marks >= 60) {
  console.log("Grade B");
} else {
  console.log("Grade C");
}

Execution order

1. First condition is checked

2. If false → next else if runs

3. If all fail → else runs

Only one block executes.

---

4. The switch Statement

4

The switch statement is used when we compare one value against multiple cases.

Example

let day = 2;

switch(day) {
  case 1:
    console.log("Monday");
    break;

  case 2:
    console.log("Tuesday");
    break;

  case 3:
    console.log("Wednesday");
    break;

  default:
    console.log("Invalid day");
}

Why break is important

break stops the switch after a match.

Without it, JavaScript continues executing the next cases (fall-through).

---

When to Use switch vs if-else

Situation	Best Choice
Checking ranges (age, marks, price)	if-else
Comparing one value with many options	switch
Complex conditions	if-else

Example:

• Marks grading → if-else

• Day of week → switch

---

Assignment

1️⃣ Check Number Type

Write a program to check whether a number is positive, negative, or zero.

let num = 5;

if (num > 0) {
  console.log("Positive");
} else if (num < 0) {
  console.log("Negative");
} else {
  console.log("Zero");
}

---

2️⃣ Print Day Using Switch

let day = 3;

switch(day) {
  case 1:
    console.log("Monday");
    break;
  case 2:
    console.log("Tuesday");
    break;
  case 3:
    console.log("Wednesday");
    break;
  default:
    console.log("Invalid Day");
}

Explain why you used if-else or switch in your solution.