JavaScript if...else Statement

🔹 What is if...else in JavaScript?

In JavaScript, the if...else statement is used to perform conditional execution. This means that the program will decide which code to execute based on a condition. If the condition is true, one block of code runs; if it's false, another block (if provided) may run instead.

🔹 1. The if Statement

The if statement executes a block of code only when the given condition is true. If the condition is false, the block is skipped.

✅ Example:

let temperature = 30;

if (temperature > 25) {
    console.log("It's a hot day!");
}

📌 In this case, since temperature is greater than 25, the message "It's a hot day!" will be printed. If temperature were 25 or lower, nothing would happen.

🔹 2. The if...else Statement

The if...else statement provides an alternative block to execute when the condition is false.

✅ Example:

let temperature = 20;

if (temperature > 25) {
    console.log("It's a hot day!");
} else {
    console.log("It's a cool day.");
}

📌 Since temperature is 20, the condition is false, so the else block executes, displaying "It's a cool day."

🔹 3. The if...else if...else Statement

When you have multiple conditions to check, you can use the else if statement.

✅ Example:

let score = 85;

if (score >= 90) {
    console.log("Grade: A");
} else if (score >= 75) {
    console.log("Grade: B");
} else if (score >= 50) {
    console.log("Grade: C");
} else {
    console.log("Grade: F");
}

📌 The program checks conditions from top to bottom. Since score = 85, the second condition (score >= 75) is true, so "Grade: B" is printed.

🔹 4. Using if with Logical Operators

JavaScript provides logical operators (&&, ||, !) to combine multiple conditions.

✅ Example:

let age = 20;
let hasID = true;

if (age >= 18 && hasID) {
    console.log("You are allowed to enter.");
} else {
    console.log("Entry denied.");
}

📌 Here, both conditions must be true for access. If age is below 18 or hasID is false, entry is denied.

🔹 5. Nested if Statements

You can place if statements inside other if statements for more complex conditions.

✅ Example:

let age = 25;
let hasTicket = true;

if (age >= 18) {
    if (hasTicket) {
        console.log("You can watch the movie.");
    } else {
        console.log("You need a ticket to enter.");
    }
} else {
    console.log("You are too young to watch the movie.");
}

📌 If age >= 18, it checks for hasTicket. If both conditions are true, the user can watch the movie.

🔹 Conclusion

• The if statement runs a block only if a condition is true.
• The if...else statement provides an alternative block when the condition is false.
• The if...else if...else statement checks multiple conditions in order.
• Logical operators (&&, ||, !) help check multiple conditions together.
• Nested if statements allow more complex decision-making.