If Statement in JavaScript

In this tutorial, we will learn about if statements in JavaScript. We will cover the basics of conditional execution using if statements.

What is an If statement

An if statement is a conditional statement that executes a block of code if a specified condition is true.

Syntax

The syntax for the if statement in JavaScript is:

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

The if statement evaluates the specified condition. If the condition is true, the code block inside the if statement is executed; otherwise, it is skipped.

The following is the flowchart of how execution flows from start to the end of an if statement.

Flowchart of If Statement

Example 1: Checking if a Number is Even

  1. Declare a variable num.
  2. Assign a value to num.
  3. Use an if statement to check if num is even.
  4. Print a message indicating whether num is even or not.

JavaScript Program

let num = 10;
if (num % 2 === 0) {
    console.log(`${num} is even.`);
}

Output

10 is even.

Example 2: Checking if a String Starts with a Specific Value

  1. Declare a variable str.
  2. Assign a value to str.
  3. Use an if statement to check if str starts with a specific value.
  4. Print a message indicating the result of the check.

JavaScript Program

let str = 'Hello, world!';
if (str.startsWith('Hello')) {
    console.log("String starts with 'Hello'.");
}

Output

String starts with 'Hello'.

Example 3: Checking if a Number is Positive

  1. Declare a variable num.
  2. Assign a value to num.
  3. Use an if statement to check if num is positive.
  4. Print a message indicating whether num is positive or not.

JavaScript Program

let num = -5;
if (num > 0) {
    console.log(`${num} is positive.`);
}

Output