DESCRIPTION
The if/else statement executes a block of code if a specified condition is true. If the condition is false, another block of code can be executed. This statement is a part of JavaScript’s “Conditional” Statements, which are used to perform different actions based on different conditions.
JavaScript supports the following forms of If…else –
- if statement
- if…else statement
- if…else if… statement.
If Statement
The if statement is the fundamental control statement that allows JavaScript to make decisions and execute statements conditionally.
Syntax –
if (expression) {
Statement(s) to be executed if expression is true
}
Example –
<html>
<body>
<script type="text/javascript">
var age = 20;
if (age > 18) {
document.write("<b>You can Vote.</b>");
}
</script>
</body>
</html>
This Code will produce the following result on your webpage –
If…else Statement
The ‘if…else’ statement is the next form of control statement that allows JavaScript to execute statements in a more controlled way.
Syntax-
if (expression) {
Statement(s) to be executed if expression is true
} else {
Statement(s) to be executed if expression is false
}
Example –
<html>
<body>
<script type="text/javascript">
var age = 15;
if (age > 18) {
document.write("<b>You can Vote.</b>");
} else {
document.write("<b>You are not eligible to vote.</b>");
}
</script>
</body>
</html>
This Code will produce the following result on your webpage –
If..else..if Statement
The if…else if… statement is an advanced form of if…else that allows JavaScript to make a correct decision out of several conditions.
Syntax –
if (expression 1) {
Statement(s) to be executed if expression 1 is true
} else if (expression 2) {
Statement(s) to be executed if expression 2 is true
} else if (expression 3) {
Statement(s) to be executed if expression 3 is true
} else {
Statement(s) to be executed if no expression is true
}
Example –
<html>
<body>
<script type="text/javascript">
var book = "maths";
if (name == "history") {
document.write("<b>History Book</b>");
} else if (book == "maths") {
document.write("<b>Maths Book</b>");
} else if (book == "economics") {
document.write("<b>Economics Book</b>");
} else {
document.write("<b>Unknown Book</b>");
}
</script>
</body>
<html>
This Code will produce the following result on your webpage –
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