Question

In Javascript, like setInterval(draw,20) you don’t include anything like in C#. You can just use the function. The function is on the Windows object of the browser.

1. Can the following objects and its functions be called without any pre-definitions?

   Window
   Navigator
   Screen
   History
   Location
   

2. Does JavaScript has any built-in functions?

Answer 1

In Javscript, there are certain things which are part of the language and will also be there. Native objects, like Array(), String() and Number(). (Not a complete list). These need no prefix in front of them, because there are none.

In addition, when running on the browser the host environment provides a global variable called window that is the same as the anonymous Javascript global that everything runs in. Methods of the window object include things like alert() and setTimeout()

Alert can be called with window.alert() or more often by just alert() itself. (Some people consider calling window.alert() best practice to a) show you are calling the global function and b) protect you from any local variables named alert.)

Clarification:

The Javascript engine keeps a global variable with no name and not normally accessible. When not running in struct mode, undeclared variables are created as properties in this global object, all global functions are put in the global object and this normally called functions points to the global object.

When running in the browser, window is the global object.