<!DOCTYPE html>
<html>
<body>
<p>The in operator returns true if the specified property is in the specified object.</p>
<p id="demo"></p>
<script>
// Arrays
var cars = ["Saab", "Volvo", "BMW"];
// Objects
var person = {firstName:"John", lastName:"Doe", age:50};
document.getElementById("demo").innerHTML =
("Saab" in cars) + "<br>" +
(0 in cars) + "<br>" +
(1 in cars) + "<br>" +
(4 in cars) + "<br>" +
("length" in cars) + "<br>" +
("firstName" in person) + "<br>" +
("age" in person) + "<br>" +
// Predefined objects
("PI" in Math) + "<br>" +
("NaN" in Number) + "<br>" +
("length" in String);
</script>
</body>
</html>