What is if Statement in JavaScript

What is an if Statement in JavaScript?

An if statement in JavaScript is a fundamental control structure that allows code to execute only if a specified condition evaluates to true. If the condition is false, the code inside the if block is skipped.

Syntax of if Statement

if (condition) {
    // Code to execute if the condition is true
}

How to Use an if Statement

1. Define a Condition – The condition inside the parentheses (()) is evaluated.
2. Execute Code – If the condition is true, the code block within the curly braces ({}) runs.
3. Skip if False – If the condition is false, the code block is bypassed.

Example:

let age = 20;

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

Output:

You are eligible to vote.

If age were less than 18, nothing would appear because the condition would not be satisfied.

Why Use if Statements?

1. Decision Making – if statements allow programs to make decisions based on user input, data, or other variables.
2. Control Flow – They help direct the flow of the program by executing certain parts of the code selectively.
3. Validation – Useful for form validation, error checks, and ensuring specific conditions are met.
4. Dynamic Behavior – if statements enable responsive, interactive websites and applications by reacting to different scenarios.

When to Use if Statements?

• Conditional Execution – When a task should only run under specific circumstances.
• User Input – Check if a form is filled correctly or if a user is authorized.
• Calculations – Perform operations based on variable values.
• Form Validation – Verify data before submission.
• Error Handling – Prevent errors by running checks before executing certain logic.

Real-World Example:

Checking Even or Odd Numbers

let number = 7;

if (number % 2 === 0) {
    console.log(number + " is even.");
}

Since 7 is not divisible by 2, nothing will print.

Example with else for Full Control

let number = 7;

if (number % 2 === 0) {
    console.log(number + " is even.");
} else {
    console.log(number + " is odd.");
}

Output:

7 is odd.

Nested if Statements

if statements can be nested to check multiple conditions.

let isLoggedIn = true;
let isAdmin = false;

if (isLoggedIn) {
    if (isAdmin) {
        console.log("Welcome, Admin.");
    } else {
        console.log("Welcome, User.");
    }
}

Output:

Welcome, User.

Advantages of if Statements

• Simple and Easy to Implement – Basic conditional checks are easy to write.
• Readable – Clear and intuitive to understand for beginners.
• Flexible – Can handle a wide range of conditions and scenarios.

Common Mistakes to Avoid

1. Omitting Braces – Always use {} even for single-line statements to avoid errors.

if (x > 10) 
    console.log("Greater");  // Works but can lead to bugs

2. Assignment Instead of Comparison

if (x = 10)  // Incorrect: assigns 10 to x instead of comparing

Fix:

if (x === 10)  // Correct: compares x to 10

3. Complex Conditions – Simplify with logical operators (&&, ||).

if (age > 18 && country === "US") {
    console.log("Eligible to vote.");
}

Key Takeaways

• The if statement executes code conditionally based on whether a condition is true.
• It’s a core part of creating dynamic, interactive websites and applications.
• Use if statements to validate, filter, and manage data dynamically.