Conditional Statements

The JavaScript if-else statement is used to execute the code whether condition is true or false. There are three forms of if statement in JavaScript.

Conditional statements are used to perform different actions based on different conditions.

Very often when you write code, you want to perform different actions for different decisions.

You can use conditional statements in your code to do this.

In JavaScript we have the following conditional statements:

Use if to specify a block of code to be executed, if a specified condition is true
Use else to specify a block of code to be executed, if the same condition is false
Use else if to specify a new condition to test, if the first condition is false
Use switch to specify many alternative blocks of code to be executed

Table of Contents

The if Statement

Use the if statement to specify a block of JavaScript code to be executed if a condition is true.

Syntax :


if (condition) {
    // the body of if
}

Example :


// check if the number is positive

const number = prompt("Enter a number: ");

// check if number is greater than 0
if (number > 0) {
 // the body of the if statement
  console.log("The number is positive");
}

Output :


Enter a number: 5
The number is positive

Suppose the user entered 5. In this case, the condition number > 0 evaluates to true. And, the body of the if statement is executed.


Enter a number: -5

Suppose the user entered –5. In this case, the condition number > 0 evaluates to false. Hence, the body of the if statement is skipped.

The else Statement

Use the else statement to specify a block of code to be executed if the condition is false.

Syntax :


if (condition) {
  //  block of code to be executed if the condition is true
} else {
  //  block of code to be executed if the condition is false
}

Example :

If the hour is less than 18, create a “Good day” greeting, otherwise “Good evening”:


if (hour < 18) {
  greeting = "Good day";
} else {
  greeting = "Good evening";
}

The else if Statement

Use the else if statement to specify a new condition if the first condition is false.

Syntax :


if (condition1) {
  //  block of code to be executed if condition1 is true
} else if (condition2) {
  //  block of code to be executed if the condition1 is false and condition2 is true
} else {
  //  block of code to be executed if the condition1 is false and condition2 is false
}

Example :

If time is less than 10:00, create a “Good morning” greeting, if not, but time is less than 20:00, create a “Good day” greeting, otherwise a “Good evening”:


if (time < 10) {
  greeting = "Good morning";
} else if (time < 20) {
  greeting = "Good day";
} else {
  greeting = "Good evening";
}