Window Events

The Window object supports many events. Unfortunately, many of these are proprietary. The safe cross-browser window events include onblur, onerror, onfocus, onload, onunload, and onresize and are detailed in Table 12-2.

Table 12-2: Common Window Events
Event	Description
onblur	Fires when the window loses focus.
onerror	Rudimentary error handling event fired when a JavaScript error occurs.
onfocus	Fires when the window gains focus.
onload	Fires when the document is completely loaded into the window. Warning: Timing of this event is not always exact.
onresize	Event triggered as user resizes the window.
onunload	Triggered when the document is unloaded, such as following an outside link or closing the window.

Adding Window events handlers can be set through HTML event attributes on the <<body>> element like so,

<<body onload="alert('entering window');" onunload="alert('leaving window')">>

or by registering events through the Window object:

function sayHi() { alert('hi'); }
function sayBye() { alert('bye'); }
window.onload = sayHi;
window.onunload = sayBye;

Internet Explorer and Netscape add numerous events to the Window object. A few of the more useful ones are detailed in Table 12-3. A general discussion of Window events can be found in Chapter 11 with a complete listing in Appendix B.

Table 12-3: Useful Extended Window Events
Event	Description
onafterprint	Event triggered after the window is printed.
onbeforeprint	Fires just before the window is printed or print previewed.
onbeforeunload	The event is triggered just before the window unloads. Should happen before the onunload event.
ondragdrop	Is triggered when a document is dragged onto a window. (Netscape only.)
onhelp	Fires when the Help key, generally F1, is clicked.
onresizeend	Fires when the resize process ends—usually the user has stopped dragging the corner of a window.
onresizestart	Fires when the resize process begins—usually the user has started dragging the corner of a window.
onscroll	Fires when the window is scrolled in either direction.