There are three definitions for routers on the web: For the network layer, the router is a networking device that decides where to direct data packets . For a Single-page application in the application layer, a router is a library that decides what web page is presented by a given URL . This middleware module is used for all URL functions, as these are given a path to a file that is rendered to open the next page. In the implementation of an API in a service layer, a router is a software component that parses a request and directs or routes the request to various handlers within a program. The router code usually accepts a response from the handler and facilitates its return to the requester.