| You might have noticed that I declared the function displayMessage as displayMessage(e) in the previous example. Why did I indicate that this function would be passed an argument? The answer is that it is passed an argument in the Netscape Navigator. This argument is an object of the event class, and you can get information about the event (such as where a mouse click occurred) using this object, which I've named e . You'll find the using this object, which I've named e . You'll find the properties of the event class in Netscape Navigator in Table 6-7. However, Internet Explorer handles things differently, of course. In Internet Explorer, event-handling functions are not passed an event object. (JavaScript is flexible enough that even if you declare a function as we have here to handle both browsers, as though it does receive an argumentalthough it really doesn'tthere's no problem.) Instead of passing an event object to event-handling functions, you use the window.event object (that is, the event subobject of the window object), which is available globally in code and doesn't have to be passed to a function. You'll find the properties of the window.event property in Internet Explorer in Table 6-8. Table 6-7. Netscape Navigator's Event Object Properties | Property | Means | | data | Holds an array of strings containing the URLs of the dropped objects. It is used with the dragdrop event. | | height | Holds a height associated with the event. | | layerX | Holds the cursor's horizontal position in pixels, relative to the layer in which the event occurred. | | layerY | Holds the cursor's vertical position in pixels, relative to the layer in which the event occurred. | | modifiers | Holds modifier keys associated with a mouse or key event. Possible values are ALT_MASK , CONTROL_MASK , SHIFT_MASK , and META_MASK . | | pageX | Holds the cursor's horizontal position in pixels, relative to the page. | | pageY | Holds the cursor's vertical position in pixels, relative to the page. | | screenX | Holds the cursor's horizontal position in pixels, relative to the screen. | | screenY | Holds a vertical position in pixels, relative to the screen. | | type | Holds the type of event. | | which | Indicates the mouse button that was pressed or the ASCII value of a pressed key. | | width | Holds a width associated with the event. | Table 6-8. Internet Explorer's window. event Object Properties | Property | Means | | altKey | Is true if the Alt key was down | | altLeft | Is true if the left Alt key was down | | button | Specifies which mouse button, if any, was pressed | | cancelBubble | Indicates whether this event should move up the event hierarchy | | clientX | Holds an x coordinate with respect to the client area | | clientY | Holds a y coordinate with respect to the client area | | ctrlKey | Is true if the Ctrl key was down | | ctrlLeft | Is true if the left Ctrl key was down | | fromElement | Specifies an element being moved | | keyCode | Holds the code of the struck key | | offsetX | Holds a container-relative x position | | offsetY | Holds a container-relative y position | | reason | Holds information about a data transfer | | returnValue | Specifies the return value of the event | | screenX | Holds an x coordinate relative to physical screen size | | screenY | Holds a y coordinate relative to physical screen size | | shiftKey | Is true if the Shift key was down | | shiftLeft | Is true if the left Shift key was down | | srcElement | Holds the element that caused the event | | srcFilter | Holds a filter event if this is a filterChange event | | toElement | Specifies the element being moved to | | type | Property event type as a string | | x | Holds an x position of the event in context | | y | Holds a y position of the event in context | For an example that uses the event objects in Tables 6-7 and 6-8, see the next section. |
