Control Flow in JavaScript: If, Else, and Switch

In the previous blog of this JavaScript series, we explored JavaScript Operators: The Basics You Need to Know and learned how operators help us perform calculations, comparisons, and logical checks.

But once we can compare values, the next question is:

How does a program decide what code should run and what should not?

This is where control flow comes in.

Control flow allows a program to make decisions and execute different code depending on conditions.

Just like in real life, we make decisions based on situations.

For example:

• If it rains → take an umbrella
• If you are hungry → eat food
• If you finish work → relax

Programs work in a similar way.

In this article, we will learn how JavaScript handles decisions using:

• if
• if...else
• else if
• switch

What is Control Flow?

Control flow refers to the order in which statements are executed in a program.

Normally, JavaScript executes code line by line from top to bottom.

Example:

console.log("Step 1");
console.log("Step 2");
console.log("Step 3");

Output

Step 1
Step 2
Step 3

But sometimes we want code to run only if a condition is true.

This is where conditional statements help us control the program flow.

The if Statement

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

Syntax

if (condition) {
    // code to execute
}

Example

Let's check if someone is eligible to vote.

let age = 20;

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

Output

You are eligible to vote.

Here:

age >= 18

If the condition is true, the code inside the block runs.

The if...else Statement

Sometimes we want to run one block of code if the condition is true and another if it is false.

This is where if...else is used.

Syntax

if (condition) {
    // runs if condition is true
} else {
    // runs if condition is false
}

Example

let age = 16;

if (age >= 18) {
    console.log("You can vote.");
} else {
    console.log("You are too young to vote.");
}

Output

You are too young to vote.

In JavaScript, you don't always need a comparison operator like age >= 18. JavaScript can evaluate any variable as a boolean. For example:

let username = "Alice";

if (username) {
    // This runs because a non-empty string is "truthy"
    console.log("Welcome, " + username);
}

The else if Ladder

Sometimes we need to check multiple conditions.

For that, we use else if.

Example: Checking Marks

let marks = 75;

if (marks >= 90) {
    console.log("Grade: A");
} else if (marks >= 70) {
    console.log("Grade: B");
} else if (marks >= 50) {
    console.log("Grade: C");
} else {
    console.log("Fail");
}

Output

Grade: B

The program checks conditions from top to bottom.

Once a condition is true, the rest are skipped.

Example Program: Positive, Negative, or Zero

Let’s write a simple program to determine the type of a number.

let number = -5;

if (number > 0) {
    console.log("Positive number");
} else if (number < 0) {
    console.log("Negative number");
} else {
    console.log("The number is zero");
}

Output

Negative number

Here we used an if–else if ladder because we had multiple possible conditions.

The switch Statement

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

Syntax

switch (expression) {
    case value1:
        // code
        break;

    case value2:
        // code
        break;

    default:
    // code
}

Example: Day of the Week

let day = 3;

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

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

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

    case 4:
        console.log("Thursday");
        break;

    case 5:
        console.log("Friday");
        break;

    case 6:
        console.log("Saturday");
        break;

    case 7:
        console.log("Sunday");
        break;

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

Output

Wednesday

Why break is Important

Inside a switch, the break statement stops execution.

Without break, JavaScript will continue running the next cases.

Example without break:

let day = 1;

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

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

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

Output

Monday
Tuesday
Wednesday

This happens because switch keeps executing cases until it finds a break.

When to Use switch vs if...else

Situation	Recommended
Checking ranges (age, marks, numbers)	if...else
Comparing one value with many fixed options	switch

Example:

marks > 80 → if-else
day = Monday/Tuesday/Wednesday → switch

Final Thoughts

Control flow is what makes programs smart and dynamic.

Using if, else, else if, and switch, we can make our programs:

• Take decisions
• Handle multiple conditions
• Execute different logic based on data

These concepts are used everywhere in real applications.

In the next article of this JavaScript series, we will explore another important concept that allows programs to repeat tasks automatically.