openshift-docs/modules/serverless-typescript-functions-context-objects.adoc

[id="serverless-typescript-functions-context-objects_{context}"]
= TypeScript context objects

Functions are invoked with a `context` object as the first parameter.

.Example context object
[source,javascript]
----
function handle(context:Context): string
----

This object provides access to the incoming HTTP request information, including the HTTP request method, any query strings or headers sent with the request, the HTTP version, and the request body. Incoming requests that contain a CloudEvent attach the incoming instance of the CloudEvent to the context object so that it can be accessed by using `context.cloudevent`.

[id="serverless-typescript-functions-context-objects-methods_{context}"]
== Context object methods

The `context` object has a single method, `cloudEventResponse()`, that accepts a data value and returns a CloudEvent.

In a Knative system, if a function deployed as a service is invoked by an event broker sending a CloudEvent, the broker examines the response. If the response is a CloudEvent, this event is handled by the broker.

.Example context object method
[source,javascript]
----
// Expects to receive a CloudEvent with customer data
export function handle(context: Context, cloudevent?: CloudEvent): CloudEvent {
  // process the customer
  const customer = cloudevent.data;
  const processed = processCustomer(customer);
  return context.cloudEventResponse(customer)
    .source('/customer/process')
    .type('customer.processed')
    .response();
}
----

[id="serverless-typescript-functions-context-types_{context}"]
== Context types

The TypeScript type definition files export the following types for use in your functions.

.Exported type definitions
[source,javascript]
----
// Invokable is the expeted Function signature for user functions
export interface Invokable {
    (context: Context, cloudevent?: CloudEvent): any
}

// Logger can be used for structural logging to the console
export interface Logger {
  debug: (msg: any) => void,
  info:  (msg: any) => void,
  warn:  (msg: any) => void,
  error: (msg: any) => void,
  fatal: (msg: any) => void,
  trace: (msg: any) => void,
}

// Context represents the function invocation context, and provides
// access to the event itself as well as raw HTTP objects.
export interface Context {
    log: Logger;
    req: IncomingMessage;
    query?: Record<string, any>;
    body?: Record<string, any>|string;
    method: string;
    headers: IncomingHttpHeaders;
    httpVersion: string;
    httpVersionMajor: number;
    httpVersionMinor: number;
    cloudevent: CloudEvent;
    cloudEventResponse(data: string|object): CloudEventResponse;
}

// CloudEventResponse is a convenience class used to create
// CloudEvents on function returns
export interface CloudEventResponse {
    id(id: string): CloudEventResponse;
    source(source: string): CloudEventResponse;
    type(type: string): CloudEventResponse;
    version(version: string): CloudEventResponse;
    response(): CloudEvent;
}
----

[id="serverless-typescript-functions-context-objects-cloudevent-data_{context}"]
== CloudEvent data

If the incoming request is a CloudEvent, any data associated with the CloudEvent is extracted from the event and provided as a second parameter. For example, if a CloudEvent is received that contains a JSON string in its data property that is similar to the following:

[source,json]
----
{
  "customerId": "0123456",
  "productId": "6543210"
}
----

When invoked, the second parameter to the function, after the `context` object, will be a JavaScript object that has `customerId` and `productId` properties.

.Example signature
[source,javascript]
----
function handle(context: Context, cloudevent?: CloudEvent): CloudEvent
----

The `cloudevent` parameter in this example is a JavaScript object that contains the `customerId` and `productId` properties.