JavaScript If...Else Statements
Conditional statements are used to perform different actions based on different conditions.
Conditional Statements
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
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) {
block of code to be executed if the condition is true
} Note that if is in lowercase letters. Uppercase letters (If or IF) will generate a JavaScript error.
Example
Make a "Good day" greeting if the hour is less than 18:00:<!DOCTYPE html>
<html>
<body>
<p>Display "Good day!" if the hour is less than 18:00:</p>
<p id="demo">Good Evening!</p>
<script>
if (new Date().getHours() < 18) {
document.getElementById("demo").innerHTML = "Good day!";
}
</script>
</body>
</html>The result of greeting will be:Good day The else Statement
Use the else statement to specify a block of code to be executed if the condition is false.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":<!DOCTYPE html>
<html>
<body>
<p>Click the button to display a time-based greeting:</p>
<button onclick="myFunction()">Try it</button>
<p id="demo"></p>
<script>
function myFunction() {
var hour = new Date().getHours();
var greeting;
if (hour < 18) {
greeting = "Good day";
} else {
greeting = "Good evening";
}
document.getElementById("demo").innerHTML = greeting;
}
</script>
</body>
</html> The result of greeting will be:Good day 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":<!DOCTYPE html>
<html>
<body>
<p>Click the button to get a time-based greeting:</p>
<button onclick="myFunction()">Try it</button>
<p id="demo"></p>
<script>
function myFunction() {
var greeting;
var time = new Date().getHours();
if (time < 10) {
greeting = "Good morning";
} else if (time < 20) {
greeting = "Good day";
} else {
greeting = "Good evening";
}
document.getElementById("demo").innerHTML = greeting;
}
</script>
</body>
</html> The result of greeting will be:Good morning 
