onreadystatechange对象发生改变时激发

Fires when the state of the object has changed.
当对象发生改变时激发。

Syntax
语法

Inline HTML <ELEMENT onreadystatechange = "handler" ... >  All platforms
Event property object.onreadystatechange = handler JScript only
object.onreadystatechange = GetRef("handler") Visual Basic Scripting Edition (VBScript) 5.0 or later only
Named script <SCRIPT FOR = object EVENT = onreadystatechange>  Internet Explorer only

Event Information

Bubbles No
Cancels No
To invoke Change the ready state. 
Default action Signals the ready state of the document. 

Event Object Properties

Although event handlers in the DHTML Object Model do not receive parameters directly, a handler can query an event object for data.

Show Available Properties

altKey Sets or retrieves a value that indicates the state of the ALT key. 
altLeft Sets or retrieves a value that indicates the state of the left ALT key.
ctrlLeft Sets or retrieves the state of the left CTRL key. 
shiftLeft Retrieves the state of the left SHIFT key. 
srcElement Sets or retrieves the object that fired the event. 
type Sets or retrieves the event name from the event object. 

Remarks

You can use the readyState property to query the current state of the element when the onreadystatechange event fires.

All elements expose an onreadystatechange event. The following objects always fire the event because they load data: applet, document, frame, frameSet, iframe, img, link, object, script, and xml elements. Other objects will only fire the onreadystatechange event when a DHTML Behavior is attached.

When working with behaviors, wait for the onreadystatechange event to fire and verify that the readyState property of the element is set to complete to ensure that the behavior is completely downloaded and applied to the element. Until the onreadystatechange event fires, if you use any of the behavior-defined members before attaching the behavior to the element, a scripting error can result, indicating that the object does not support that particular property or method.

Example

This example uses the onreadystatechange event to invoke a function when the readyState is complete.

HideExample

document.onreadystatechange=fnStartInit;
function fnStartInit()
{
if (document.readyState=="complete")
{
// Finish initialization.
}
}

 

<script>
var img=null;
function s()
{
if(img)
img.removeNode(true);
img=document.createElement("img");
img.style.position="absolute";
img.style.visibility="hidden";
img.attachEvent("onreadystatechange",orsc);
img.attachEvent("onerror",oe);
document.body.insertAdjacentElement("beforeend",img);
img.src=inp.value;
}

function oe()
{
alert("cant load img");
}

function orsc()
{
if(img.readyState!="complete")return false;
alert("高:"+img.offsetHeight+"/n宽:"+img.offsetWidth);
}

</script>
<input type="file" Name="file" id="inp" value="默认值"><br>
<input onclick="s()" type="button" value="点我一下给出要上传图片的大小及长、宽" name="button">