The proto property of Object.prototype is an accessor property (a getter function and a setter function) that exposes the internal [[Prototype]] (either an object or null) of the object through which it is accessed.
FYI MDN says proto is being deprecated - use Object.getPrototypeOf and Object.setPrototypeOf (setter not recommended to use) instead.
Basically, when a new instance of a constructor is created, it's proto is the same as the constructor's prototype.
// Declare a function to be used as a constructor
function Employee() {
/* initialise instance */