Article Categories
- All Categories
-
Data Structure
-
Networking
-
RDBMS
-
Operating System
-
Java
-
MS Excel
-
iOS
-
HTML
-
CSS
-
Android
-
Python
-
C Programming
-
C++
-
C#
-
MongoDB
-
MySQL
-
Javascript
-
PHP
-
Economics & Finance
Selected Reading
What is the usage of in operator in JavaScript?
The in operator is used in JavaScript to check whether a property exists in an object or not. It returns true if the property is found, and false otherwise.
Syntax
propertyName in object
Basic Example
Here's how to use the in operator to check for properties in objects:
<!DOCTYPE html>
<html>
<body>
<script>
var emp = {name: "Amit", subject: "Java"};
document.write("name" in emp);
document.write("<br>");
document.write("subject" in emp);
document.write("<br>");
document.write("age" in emp);
document.write("<br>");
document.write("MAX_VALUE" in Number);
</script>
</body>
</html>
true true false true
Checking Array Indices
The in operator also works with array indices:
<!DOCTYPE html>
<html>
<body>
<script>
var fruits = ["apple", "banana", "orange"];
document.write(0 in fruits);
document.write("<br>");
document.write(2 in fruits);
document.write("<br>");
document.write(5 in fruits);
</script>
</body>
</html>
true true false
Inherited Properties
The in operator checks both own properties and inherited properties from the prototype chain:
<!DOCTYPE html>
<html>
<body>
<script>
var person = {name: "John"};
document.write("name" in person);
document.write("<br>");
document.write("toString" in person);
document.write("<br>");
document.write("hasOwnProperty" in person);
</script>
</body>
</html>
true true true
Comparison with hasOwnProperty()
| Method | Checks Own Properties | Checks Inherited Properties |
|---|---|---|
in operator |
Yes | Yes |
hasOwnProperty() |
Yes | No |
Conclusion
The in operator is a reliable way to check property existence in JavaScript objects and arrays. It checks both own and inherited properties, making it useful for comprehensive property detection.
Updated on: 2026-03-15T23:18:59+05:30
193 Views
Advertisements