JavaScript Examples Bible - UserWorks Technologies

Chapter 2 ✦ Window and Frame Objects (Chapter 16)
theTime += (theHour >= 12) ? “ pm” : “ am”
theTime += ((flasher) ? “ “ : “*”)
flasher = !flasher
window.status = theTime
// recursively call this function every second to keep timer going
timerID = setTimeout(“updateTime()”,1000)
}
//-->
In this function, the setTimeout() method works in the following way: Once the
current time (including the flasher status) appears in the statusbar, the function
waits approximately one second (1,000 milliseconds) before calling the same function
again. You don’t have to clear the timerID value in this application because
JavaScript does it for you every time the 1,000 milliseconds elapse.
A logical question to ask is whether this application should be using
setInterval() instead of setTimeout(). This is a case in which either one does
the job. To use setInterval() here would require that the interval process start
outside of the updateTime() function, because you need only one process running
that repeatedly calls updateTime(). It would be a cleaner implementation in that
regard, instead of the tons of timeout processes spawned by Listing 16-38. On the
other hand, the application would not run in any browsers before NN4 or IE4, as
Listing 16-38 does.
To demonstrate passing parameters, you can modify the updateTime() function
to add the number of times it gets invoked to the display in the statusbar. For that
to work, the function must have a parameter variable so that it can catch a new
value each time it is invoked by setTimeout()’s expression. For all browsers, the
function would be modified as follows (unchanged lines are represented by the
ellipsis):
function updateTime(i) {
...
window.status = theTime + “ (“ + i + “)”
// pass updated counter value with next call to this function
timerID = setTimeout(“updateTime(“ + i+1 + “)”,1000)
}
If you were running this exclusively in NN4+, you could use its more convenient way
of passing parameters to the function:
timerID = setTimeout(updateTime,1000, i+1)
In either case, the onLoad event handler would also have to be modified to get the
ball rolling with an initial parameter:
onLoad = “updateTime(0)”
177
windowObject.setTimeout()