JavaScript Examples Bible - UserWorks Technologies

174
JavaScript Examples Bible: The Essential Companion to JavaScript Bible
windowObject.setInterval()
Listing 16-36: setInterval() Demonstration Frameset
setInterval() Method
In the top frame is a control panel with several buttons that control the automatic
scrolling of the Bill of Rights text document in the bottom frame. Listing 16-37 shows
the control panel document. Many functions here control the interval, scrolling jump
size, and direction, and they demonstrate several aspects of applying setInterval().
Notice that in the beginning the script establishes a number of global variables.
Three of them are parameters that control the scrolling; the last one is for the ID
value returned by the setInterval() method. The script needs that value to be a
global value so that a separate function can halt the scrolling with the
clearInterval() method.
All scrolling is performed by the autoScroll() function. For the sake of simplicity,
all controlling parameters are global variables. In this application, placement of
those values in global variables helps the page restart autoscrolling with the same
parameters as it had when it last ran.
Listing 16-37: setInterval() Control Panel
ScrollBy Controller
var scrollSpeed = 500
var scrollJump = 1
var scrollDirection = “down”
var intervalID
function autoScroll() {
if (scrollDirection == “down”) {
scrollJump = Math.abs(scrollJump)
} else if (scrollDirection == “up” && scrollJump > 0) {
scrollJump = -scrollJump
}
parent.display.scrollBy(0, scrollJump)
if (parent.display.pageYOffset