It is pretty obvious thing that web application passes data to user in different form. Its not the only one way transaction,sometimes user also need to parse the data to the server in form of login credentials, registration, file upload etc..
One way of transmitting data which are not modifiable directly at client side is Hidden HTML Form Fields. While creating a webpage some fields are created in with hidden type so that it wont be appear at client side but everyone will be interacting with that indirectly. To illustrate this lets take an example.
Let's suppose any online purchasing website. If customer is going to buy a product then only modifiable value at client side will be quantity only. How much quantity a customer is going to buy that has to be filled by client only. If customer selects quantity 2 so there will be a function at client side that price will be multiplied by the quantity and will be displayed on the screen. Thus how whole payment transaction is carried away. In this case price field's value is written hidden type in html page rather than normal one. Because website owner does not want customer to change prize it has to be static. So that remains hidden not modifiable.