The Express API consists of various methods and properties on the request and response objects. These are inherited by prototype. There are two extension points for the Express API:

1. The global prototypes at express.request and express.response.
2. App-specific prototypes at app.request and app.response.

Altering the global prototypes will affect all loaded Express apps in the same process. If desired, alterations can be made app-specific by only altering the app-specific prototypes after creating a new app.

Methods

You can override the signature and behavior of existing methods with your own, by assigning a custom function.

Following is an example of overriding the behavior of res.sendStatus.

app.response.sendStatus = function (statusCode, type, message) {
  // code is intentionally kept simple for demonstration purpose
  return this.contentType(type)
    .status(statusCode)
    .send(message)
}

The above implementation completely changes the original signature of res.sendStatus. It now accepts a status code, encoding type, and the message to be sent to the client.

The overridden method may now be used this way:

res.sendStatus(404, 'application/json', '{"error":"resource not found"}')