Code on demand (optional)

As the phrase code on demand suggests, the service may try to execute code on the client to extend the functionality. However, this is optional, and not every service does this.

Consider an example of a web application that calls a ticketing service to fetch all the available tickets. The service wants always to show this information in an alert. In order to do this, the service can return a JavaScript code along with the data, which has an alert message with the number of available tickets. Thus, as soon as the client receives the response from the service, an alert is executed and the data is shown.