mode

Request: Mode.

Specifies the operating mode for this request, which is derived from the source of the request and applicable security context. This property is typically not used server-side.

From MDN: "The mode read-only property of the Request interface contains the mode of the request (e.g., cors, no-cors, same-origin, navigate or websocket.) This is used to determine if cross-origin requests lead to valid responses, and which properties of the response are readable."

See also: MDN, Request.mode.