JavaScript Examples Bible - UserWorks Technologies

152
JavaScript Examples Bible: The Essential Companion to JavaScript Bible
Tip
windowObject.status
Listing 16-19 (continued)
function scrollMsg() {
// set the number of times scrolling message is to run
if (maxCount == 0) {
maxCount = 3 * msg.length
}
window.status = msg
// keep track of how many characters have scrolled
currCount++
// shift first character of msg to end of msg
msg = msg.substring (1, msg.length) + msg.substring (0, 1)
// test whether we’ve reached maximum character count
if (currCount >= maxCount) {
timerID = 0 // zero out the timer
window.status = “” // clear the status bar
return // break out of function
} else {
// recursive call to this function
timerId = setTimeout(“scrollMsg()”, delay)
}
}
// -->
Because the statusbar is being set by a standalone function (rather than by an
onMouseOver event handler), you do not have to append a return true statement to
set the status property. The scrollMsg() function uses more advanced JavaScript
concepts, such as the window.setTimeout() method (covered later in this chapter)
and string methods (covered in Chapter 34 of the JavaScript Bible). To speed the pace
at which the words scroll across the statusbar, reduce the value of delay.
Many Web surfers (myself included) don’t care for these scrollers that run forever
in the statusbar. Rolling the mouse over links disturbs the banner display.
Scrollers can also crash earlier browsers, because the setTimeout() method eats
application memory in Navigator 2. Use scrolling bars sparingly or design them to
run only a few times after the document loads.
Setting the status property with onMouseOver event handlers has had a checkered
career along various implementations in Navigator. A script that sets the statusbar
is always in competition against the browser itself, which uses the statusbar
to report loading progress. When a “hot” area on a page is at the edge of a frame,
many times the onMouseOut event fails to fire, thus preventing the statusbar from
clearing itself. Be sure to torture test any such implementations before declaring
your page ready for public access.