JavaScript Global Objects Reference
Jonathan Reid, Thomas Valentine · Apress eBooks · 2013
Since one of the basic features of JavaScript is prototypal inheritance, it has no base classes for things like arrays or strings. Instead, JavaScript has a set of base objects from which other objects of the same type can inherit their properties and methods. These base objects reside in the global scope (which in the browser is the window object) and can thus be accessed at any time.