JavaScript Switch Case and While Loops

Introduction To JavaScript Control Structures

In JavaScript, control structures are used to determine how your program flows — meaning which code runs and when. Two important control structures are:

• Switch Case (used for decision making)
• While Loops (used for repeating actions)

Switch Case In JavaScript

What Is A Switch Case?

A switch case is used when you want to check a single value against multiple possible options. It is often cleaner and easier to read than using many if...else statements.

How It Works

• The switch takes an expression (a value).
• It compares that value with each case.
• When a match is found, the code inside that case runs.
• The break keyword stops further checking.
• If no match is found, the default case runs (optional).

Basic Syntax

switch (expression) {
    case value1:
        // code to run if expression === value1
        break;

    case value2:
        // code to run if expression === value2
        break;

    default:
        // code to run if no case matches
}

Example 1: Simple Switch Case

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");
}

Output:

Wednesday

Why Break Is Important

If you forget break, JavaScript will continue executing the next cases even after a match.

Example without break:

let fruit = "apple";

switch (fruit) {
    case "apple":
        console.log("This is an apple");

    case "banana":
        console.log("This is a banana");

    default:
        console.log("Unknown fruit");
}

Output:

This is an apple
This is a banana
Unknown fruit

This behavior is called fall-through.

While Loop In JavaScript

What Is A While Loop?

A while loop is used to repeat a block of code as long as a condition remains true.

How It Works

• The loop checks a condition.
• If the condition is true, the code runs.
• After running, the condition is checked again.
• This continues until the condition becomes false.

Basic Syntax

while (condition) {
    // code to execute repeatedly
}

Example 1: Counting Numbers

let i = 1;

while (i <= 5) {
    console.log(i);
    i++;
}

Output:

1
2
3
4
5

Important Concept: Avoid Infinite Loops

If the condition never becomes false, the loop will run forever. This is called an infinite loop.

Example of an infinite loop:

let i = 1;

while (i <= 5) {
    console.log(i);
    // missing i++ causes infinite loop
}

To avoid this, always make sure the loop variable changes.