JavaScript Examples Bible - UserWorks Technologies

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JavaScript Examples Bible: The Essential Companion to JavaScript Bible
The setInterval() method is invoked inside the startScroll() function.
This function initially “burps” the page by one scrollJump interval so that the test
in autoScroll() for the page being scrolled all the way to the top doesn’t halt a
page from scrolling before it gets started. Notice, too, that the function checks for
the existence of an interval ID. If one is there, it is cleared before the new one is set.
This is crucial within the design of the example page, because repeated clicking of
the Start Scrolling button triggers multiple interval timers inside the browser. Only
the most recent one’s ID would be stored in intervalID, allowing no way to clear
the older ones. But this little side trip makes sure that only one interval timer is
running. One of the global variables, scrollSpeed, is used to fill the delay parameter
for setInterval(). To change this value on the fly, the script must stop the
current interval process, change the scrollSpeed value, and start a new process.
The intensely repetitive nature of this application is nicely handled by the
setInterval() method.
setTimeout(“expr”, msecDelay [, language])
setTimeout(functionRef, msecDelay [,
funcarg1, ..., funcargn])
windowObject.setTimeout()
NN2 NN3 NN4 NN6 IE3/J1 IE3/J2 IE4 IE5 IE5.5
Compatibility ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓ ✓
Example
When you load the HTML page in Listing 16-38, it triggers the updateTime()
function, which displays the time (in hh:mm am/pm format) in the statusbar.
Instead of showing the seconds incrementing one by one (which may be distracting
to someone trying to read the page), this function alternates the last character of
the display between an asterisk and nothing, like a visual “heartbeat.”
Listing 16-38: Display the Current Time
Status Bar Clock
12) ? theHour - 12 : theHour)
theTime += ((theMin < 10) ? “:0” : “:”) + theMin