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

if (debugging)
alert("Returned from swapImage() with swapStatus="
and include alert()s marking the flow of execution in swapImages(). By examining the content
and order of the alert()s as they appear, you are granted a window to the internal state of your
script.
Because using many alert()s when debugging large or complicated scripts may be impractical
(not to mention annoying), output is often sent to another browser window instead. Using this
technique, a new window, say, debugWindow, is opened at the beginning of the script, and
debugging information is written into the window using syntax like
debugWindow.document.write() method. The only potential gotcha is that you need to wait
for the window to actually be opened before attempting to write() to it. See Chapter 12 for more
information on inter-window communication.
Stack Traces Whenever one function calls another, the interpreter must keep track of the
calling function so that when the called function returns, it knows where to continue execution.
Such records are stored in the call stack, and each entry includes the name of the calling
function, the line number of invocation, arguments to the function, and other local variable
information. For example, consider this simple code:
function a(x)
{
}
document.write(x);
function b(x)
{
}
a(x+1);
function c(x)
{
}
b(x+1);
c(10);
At the document.write in a(), the call stack looks something like this:
a(12), line 3, local variable information…