callbackobject, the FaaS would strip it from the return value, and then send the rest of the return value to the HTTP endpoint defined in the callback.
say()function returns a JSON
callback, which requests SendGrid to send the hello messages as an email. The Rust function is as follows.
callbackobject in the return value is as follows. It conforms to the Node.js request options specification.
callbackcould direct the result from one function to another, and hence chaining multiple functions together.