Tryit Editor v1.8

Source Code:

<!DOCTYPE html>
<html>
<body>
<h2>Create Object from JSON String</h3>
<p>First Name: <span id="fname"></span></p> 

<script>
var employees = [
{ "firstName" : "John" , "lastName" : "Doe" }, 
{ "firstName" : "Anna" , "lastName" : "Smith" }, 
{ "firstName" : "Peter" , "lastName" : "Jones" }, ];
employees[1].firstName="Jonatan";
document.getElementById("fname").innerHTML=employees[1].firstName;
</script>

</body>
</html>

Result:

W3Schools.com - Try it yourself

Edit the code above and click "Submit Code" to see the result.