If-Else Statement in JavaScript

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

What is an If-Else statement

An if-else statement is a conditional statement that executes one block of code if a specified condition is true, and another block of code if the condition is false.

Syntax

The syntax for the if-else statement in JavaScript is:

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

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

Flowchart of If Else Statement

Example 1: Checking if a Number is Even or Odd

  1. Declare a variable num.
  2. Assign a value to num.
  3. Use an if-else statement to check if num is even or odd.
  4. Print a message indicating whether num is even or odd.

JavaScript Program

let num = 10;
if (num % 2 === 0) {
    console.log(num + ' is even.');
} else {
    console.log(num + ' is odd.');
}

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-else 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'.');
} else {
    console.log('String does not start with 'Hello'.');
}

Output

String starts with 'Hello'.

Example 3: Checking if a Number is Positive or Negative

  1. Declare a variable num.
  2. Assign a value to num.
  3. Use an if-else statement to check if num is positive or negative.
  4. Print a message indicating whether num is positive or negative.

JavaScript Program

let num = -5;
if (num > 0) {
    console.log(num + ' is positive.');
} else {
    console.log(num + ' is negative or zero.');
}

Output

-5 is negative or zero.