Detailed explanation of how to use JS event_javascript skills

Some properties of event are only meaningful for specific events. For example, the fromElement and toElement properties are only meaningful for onmouseover and onmouseout events.

The following example checks whether the mouse is clicked on a link, and, if the shift key is pressed, cancels the link jump.

Example below Displays the current position of the mouse on the status bar.






Attributes:


altKey, button, cancelBubble, clientX, clientY, ctrlKey, fromElement, keyCode , offsetX, offsetY, propertyName, returnValue, screenX,
screenY, shiftKey, srcElement, srcFilter, toElement, type, x, y


1.altKey
Description:
Check The state of the alt key.

Syntax:
event.altKey

Possible values:
When the alt key is pressed, the value is TRUE, otherwise it is FALSE. Read only.


2.button
Description:
Check the pressed mouse button.

Syntax:
event.button

Possible values:
0 No button pressed
1 Press the left button
2 Press the right button
3 Press the left or right button
4 Press the middle key
5 Press the left and middle keys
6 Press the right and middle keys
7 Press all keys

This attribute is only used for onmousedown, onmouseup, and onmousemove event. For other events, 0 is returned regardless of the mouse status (such as onclick).

3.cancelBubble
Description:
Detects whether to accept the control of the event of the upper element.

Syntax:
event.cancelBubble[ = cancelBubble]

Possible values:
This is a readable and writable Boolean value:

TRUE is not Event control of upper-level elements.
FALSE allows to be controlled by events of upper-level elements. This is the default value.

Example:
The following code snippet demonstrates that when clicking on the image (onclick), if the shift key is also pressed at the same time, canceling the event onclick on the upper element (body). showSrc() function.












4.clientX
Description:
Returns the X coordinate of the mouse in the client area of ​​the window.

Syntax:
event.clientX

Comments:
This is a read-only property. This means that you can only use it to get the current position of the mouse, but you cannot use it to change the position of the mouse.


5.clientY
Description:
Returns the Y coordinate of the mouse in the client area of ​​the window.

Syntax:
event.clientY

Comments:
This is a read-only property. This means that you can only use it to get the current position of the mouse, but you cannot use it to change the position of the mouse.


6.ctrlKey
Description:
Check the status of the ctrl key.

Syntax:
event.ctrlKey

Possible values:
When the ctrl key is pressed, the value is TRUE, otherwise it is FALSE. Read only.


7.fromElement
Description:
Detect the element that the mouse leaves when the onmouseover and onmouseout events occur. Reference: 18.toElement

Syntax:
event.fromElement

Comments:
This is a read-only property.


8.keyCode
Description:
Detects the internal code corresponding to keyboard events.
This attribute is used for onkeydown, onkeyup, and onkeypress events.

Syntax:
event.keyCode[ = keyCode]


Possible values:
This is a readable and writable value, which can be any Unicode keyboard internal code . If no keyboard event is raised, the value is 0 .


9.offsetX
Description:
Checks the horizontal coordinate of the mouse position relative to the object that triggered the event

Syntax:
event.offsetX


10.offsetY
Description:
Checks the vertical coordinate of the mouse position relative to the object that triggered the event

Syntax:
event.offsetY


11.propertyName
Description:
Sets or returns the name of the element's changed property.

Syntax:
event.propertyName [ = sProperty ]

Possible values:
sProperty is a string that specifies or returns the element that triggered the event that changed during the event The name of the property.
This property is readable and writable. No default value.

Note:
You can get the value of propertyName by using the onpropertychange event.
<script>... <BR>function cancelLink() ...{ <BR> if (window.event.srcElement.tagName == "A" && window.event.shiftKey) <BR> window.event.returnValue = false; <BR>} <BR></script>Example: <script> <BR>function checkCancel() ...{ <BR> if (window.event.shiftKey) <BR> window.event.cancelBubble = true; <BR>} <BR>function showSrc() ...{ <BR> if (window.event.srcElement.tagName == "IMG") <BR> alert(window.event.srcElement.src); <BR>} <BR></script>The following example uses the onpropertychange event to pop up a dialog box to display the value of propertyName.

 


<script>... <BR>function changeProp()...{ <BR> btnProp.value = "This is the new VALUE"; <BR>} <br><br>function changeCSSProp()...{ <BR> btnStyleProp.style.backgroundColor = "aqua"; <BR>} <BR></script>

The event object property propertyName is
used here to return which property has been
altered.

VALUE="Click to change the VALUE property of this button"
onpropertychange='alert(event.propertyName+" property has changed value")'>
onclick="changeCSSProp()"
VALUE="Click to change the CSS backgroundColor property of this button"
onpropertychange='alert(event.propertyName+" property has changed value")'>







12.returnValue
描述：
设置或检查从事件中返回的值

语法：
event.returnValue[ = Boolean]

可能的值：
true 事件中的值被返回
false 源对象上事件的默认操作被取消

例子见本文的开头。


13.screenX
描述：
检测鼠标相对于用户屏幕的水平位置

语法：
event.screenX


注释：
这是个只读属性。这意味着，你只能通过它来得到鼠标的当前位置，却不能用它来更改鼠标的位置。


14.screenY
描述：
检测鼠标相对于用户屏幕的垂直位置

语法：
event.screenY

注释：
这是个只读属性。这意味着，你只能通过它来得到鼠标的当前位置，却不能用它来更改鼠标的位置。


15.shiftKey
描述：
检查shift键的状态。

语法：
event.shiftKey

可能的值：
当shift键按下时，值为 TRUE ，否则为 FALSE 。只读。


16.srcElement
描述：
返回触发事件的元素。只读。例子见本文开头。

语法：
event.srcElement


17.srcFilter
描述：
返回触发 onfilterchange 事件的滤镜。只读。

语法：
event.srcFilter


18.toElement
描述：
检测 onmouseover 和 onmouseout 事件发生时，鼠标所进入的元素。 参考：7.fromElement

语法：
event.toElement

注释：
这是个只读属性。

例子：下面的代码演示了当鼠标移到按钮上时，弹出一个对话框，显示“mouse arrived”


<script> <BR>function testMouse(oObject) ...{ <BR> if(oObject.contains(event.toElement)) ...{ <BR> alert("mouse arrived"); <BR> } <BR>} <BR></script>

Mouse Over This.



19.type
描述：
返回事件名。

语法：
event.type

注释：
返回没有“on”作为前缀的事件名，比如，onclick事件返回的type是click
只读。


20. x
描述：
返回鼠标相对于css属性中有position属性的上级元素的x轴坐标。如果没有css属性中有position属性的上级元素，默认以BODY元素作为参考对象。

语法：
event.x

注释：
如果事件触发后，鼠标移出窗口外，则返回的值为 -1
这是个只读属性。这意味着，你只能通过它来得到鼠标的当前位置，却不能用它来更改鼠标的位置。


21. y
描述：
返回鼠标相对于css属性中有position属性的上级元素的y轴坐标。如果没有css属性中有position属性的上级元素，默认以BODY元素作为参考对象。

语法：
event.y

注释：
如果事件触发后，鼠标移出窗口外，则返回的值为 -1
这是个只读属性。这意味着，你只能通过它来得到鼠标的当前位置，却不能用它来更改鼠标的位置。