JavaScript 2.0-The Complete Reference, Second ... - freecodingtutorial

There are some important subtleties regarding variable scope. The first is that each browser
window has its own global context. So it is unclear at first glance how to access and manipulate
data in other browser windows. Fortunately, JavaScript enables you to do so by providing
access to frames and other named windows. The mechanics of cross-window interaction is
covered in later chapters, particularly Chapter 12.
The second subtlety related to scoping is that, no matter where a variable is declared in a
context, it is visible throughout that context. This implies that a variable declared at the end of a
function is visible throughout the whole function. However, any initialization that is included in
the declaration is only performed when that line of code is reached. The result is that it is
possible to access a variable before it is initialized, as in the following example:
function myFunction()
{
document.writeln("The value of x before initialization in myFunction
is: ", x);
}
var x = "Hullo there!";
document.writeln("The value of x after initialization in myFunction
is: ", x);
myFunction();
The result is shown in Figure 3-3. Note how scope has undefined value before it is initialized.
Figure 3-3: Variables may be visible without yet being initialized.
The third subtlety has to do with static scoping. Consider the following code,
var scope = "global";
function outerFunction()
{
var scope = "local";
innerFunction();