If, Else If, and Else Statements

Every program needs to make decisions.
For example:

• If age is above 18 ? allow login

• If marks are high ? show “Pass”

• If the item is out of stock ? show error

• If username is empty ? show warning

JavaScript uses if, else if, and else statements to perform these decisions.

This chapter will help you understand how to use them confidently.

What Is an if Statement?

An if statement checks a condition.
If the condition is true, the code inside runs.

Syntax:

if (condition) {
    // code to run when condition is true
}

Example 1: Simple if Statement

let age = 20;

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

Output:

You are eligible.

What Is an else Statement?

The else block runs when the if condition is false.

Example:

let marks = 30;

if (marks >= 35) {
    console.log("Pass");
} else {
    console.log("Fail");
}

Output:

Fail

What is else if?

Use else if when you have multiple conditions to check.

Example:

let score = 75;

if (score >= 90) {
    console.log("Grade A");
} else if (score >= 75) {
    console.log("Grade B");
} else if (score >= 60) {
    console.log("Grade C");
} else {
    console.log("Grade D");
}

Output:

Grade B

Example: Checking Temperature

let temp = 15;

if (temp > 30) {
    console.log("Hot");
} else if (temp > 20) {
    console.log("Warm");
} else {
    console.log("Cold");
}

Output:

Cold

Multiple Conditions Using && and ||

Example with AND (&&)

let age = 19;
let id = true;

if (age >= 18 && id) {
    console.log("Entry allowed");
}

Output:

Entry allowed

Example with OR (||)

let day = "Sunday";

if (day === "Saturday" || day === "Sunday") {
    console.log("Weekend");
}

Output:

Weekend

Nested if Statements (if inside if)

let username = "aman";
let password = "1234";

if (username === "aman") {
    if (password === "1234") {
        console.log("Login successful");
    } else {
        console.log("Wrong password");
    }
} else {
    console.log("User not found");
}

Output:

Login successful

Real-Life Example: Shopping Discount

let amount = 1200;

if (amount >= 2000) {
    console.log("Discount: 20%");
} else if (amount >= 1000) {
    console.log("Discount: 10%");
} else {
    console.log("No discount");
}

Output:

Discount: 10%

Real-Life Example: Eligibility Check

let age = 17;

if (age >= 18) {
    console.log("Eligible for voting");
} else {
    console.log("Not eligible");
}

Example Program (Complete Decision Tree)

let marks = 82;

if (marks >= 90) {
    console.log("Excellent");
} else if (marks >= 75) {
    console.log("Very Good");
} else if (marks >= 50) {
    console.log("Good");
} else if (marks >= 35) {
    console.log("Pass");
} else {
    console.log("Fail");
}

Output:

Very Good

Common Mistakes Beginners Make

1. Using = instead of == or ===

2. Missing curly braces {} for multiple statements

3. Writing else if without else

4. Wrong ordering of conditions

5. Confusing logical operators