Function Execution

The process of invoking your Twilio Function code is quite simple. By design, the Twilio Function lightweight environment provides developers with all the flexibility they need. Read on to learn about how Twilio Functions runs your code.

During invocation the following steps occur:

1. Environment Bootstrap - The Twilio Function environment is bootstrapped, and any resources your Function code may rely on are quickly initialized.
2. Handler Execution - The Twilio Environment will then execute the exports.handler() method and provide the context, event and callback parameters.
3. Response Emitted - When your Twilio Function code has completed, you call the callback() method to emit your response. After executing the callback() method, your Twilio Function execution will be terminated. This includes any asynchronous processes that may still executing.

Handler Method

The handler method is the interface between Twilio Functions and your application logic. You can think of the handler method as the entry point to your application. This is somewhat analogous to a main() function in Java or __init__ in Python.

Twilio Functions will execute your handler method when it is ready to hand off control of execution to your application logic. If your Function Code does not contain a handler method, Twilio Functions will be unable to execute your logic and will emit an HTTP 500.

Handler Arguments

Context Object

Twilio Functions provides the context object as an interface between the current execution environment and the handler method. The context object provides access to environment variables and helper methods that can be accessed at execution time.

Helper Methods

The context object provides helper methods that preinitialize common utilities and clients that you might find useful when building your application. These helper methods extract all their required configuration from environment variables.

Default Environment Variables

The context object provides several environment variables by default. These default environment variables are typically required for initializing one of the helper methods.

Environmental Variables

Developers are encouraged to use Environmental Variables to separate their code from configuration. Using Twilio Functions, developers can add, remove and update Environmental Variables through the Twilio Console. Using Environmental Variables ensures that your code is portable and that simple configuration changes can be made instantly.

Event Object

The event object contains the request parameters passing into your Function. Both POST and GET parameters will be collapsed into the same object. For POST requests, you can pass either form encoded parameters or JSON documents; both will be collapsed into the event object. Currently, it is not possible to access request headers in the function execution context.

Callback Function

When you have finished processing your request, you need to invoke the callback function to emit a response and complete execution. The callback method will automatically determine the data type of your response and serialize the output appropriately.

You must invoke the callback method when your Function is done processing. Failure to invoke the callback will cause your Function to continue running up to the 5 second execution time limit. When your Function reaches the execution time limit, it will be terminated, and a 504 Gateway timeout will be returned to the client.

Callback and Asynchronous Limitations

It is important to note that when the callback function is invoked, it will terminate all execution of your Function. This includes any asynchronous processes you may have kicked off during during the execution of your handler.

For this reason, if you are using libraries that are natively asynchronous, you need to nest your call to the callback function inside the promise handler.

Callback Arguments

Constructing a Response

In some instances, your Function may need greater control over the response it is going to emit. For those instances, you can use the Twilio Response object included in your Function by default.

By using the Twilio Response object, you will be able to specify the status code, headers, and body of your response. You can begin constructing a custom response by creating a new Twilio Response object, like so:

let response = new Twilio.Response();

Twilio Response Methods