The operator is used in JavaScript to check whether a property is in an object or not.
Example
You can try to run the following code to learn how to use in operator in JavaScript −
<!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("MAX_VALUE" in Number);
document.write("<br>");
document.write("MIN" in Number);
</script>
</body>
</html>