The Compass API allows a Cordova application to determine the device’s heading along a two dimensional plane roughly corresponding with the surface of the Earth. An application would use this API to measure the device’s heading and update a compass image, map or some other aspect of the application based on the heading.
Many modern smartphones have a physical compass (on a chip) and the API simply queries the chip and returns an angle between 0 and 360 indicating the direction the device is pointing. A value of 0 indicates the device is pointing North, 90 indicates it is pointing east, 180 refers to South and 270 refers to West.
While most modern smartphones have a compass, not all of them do. iPhone devices have always had one, ...