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How to use the "in" operator in JavaScript?
In this article, we are going to explore the 'in' operator and how to use it in JavaScript. The in operator is an inbuilt operator in JavaScript that is used for checking whether a particular property exists in an object or not. It will return true if the property exists, else false is returned.
Syntax
prop in object
Parameters
This function accepts the following parameters as described below −
prop − This parameter holds the string or symbol that represents a property name or the array index.
object − This object will be checked if it contains the prop or not.
Return value − This method will return either true or false if the specified property is found in the object or not.
Example 1
In the below example, we are going to find if the property exists or not by using the ‘inin’ operator in JavaScript.
# index.html
<html>
<head>
<title>IN operator</title>
</head>
<body>
<h1 style="color: red;">
Welcome To Tutorials Point
</h1>
<script>
// Illustration of in operator
const array = ['key', 'value', 'title', 'TutorialsPoint']
// Output of the indexed number
console.log(0 in array) //true
console.log(2 in array) //true
console.log(5 in array) //false
// Output of the Value
// you must specify the index number, not the value at that index
console.log('key' in array) //false
console.log('TutorialsPoint' in array) // false
// output of the Array property
console.log('length' in array)
</script>
</body>
</html>Output
The above program will produce the following output in the Console.
true true false false false true
Example 2
In the below example, we illustrate the in operator.
# index.html
<html>
<head>
<title>IN operator</title>
</head>
<body>
<h1 style="color: red;">
Welcome To Tutorials Point
</h1>
<script>
// Illustration of in operator
const student = { name: 'Bill', class: 'IX', subjects: 'PCM', age: '16' };
console.log('name' in student);
delete student.name;
console.log('name' in student);
if ('name' in student === false) {
student.name = 'Steve';
}
console.log(student.name);
</script>
</body>
</html>Output
The above program will produce the following result in the Console.
true false Steve
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