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onreadystatechange event | readystatechange event (XMLDocument)

Browser support:

Occurs when the load state of the XMLDocument object changes.

Use the readyState property in your event handler for the onreadystatechange event to get the current state.

The onreadystatechange event and the readyState property are useful if the load method of the XMLDocument object loads an XML document asynchronously. If you want to start processing partial data as soon as it becomes available, use the ondataavailable event.

If you need the onreadystatechange event for http requests (AJAX), please see the onreadystatechange event of the XMLHttpRequest object.

How to register:

In HTML:

This event cannot be registered in HTML.

In JavaScript:

object.onreadystatechange = handler;

object.addEventListener ("readystatechange", handler, useCapture);

9

object.attachEvent ("onreadystatechange", handler);

You can find the related objects in the Supported by objects section below.

The event object is accessible to all event handlers in all browsers. The properties of the event object contain additional information about the current event. To get further details about these properties and the possible event handler registration methods, please see the page for the event object.

For a complete list of events, see the page for Events in JavaScript.

Basic information:

Bubbles	No
Cancelable	No
Event object	-

Actions that invoke the onreadystatechange event:

If the load state of the XMLDocument object has changed.

Events related to the onreadystatechange event:

The ondataavailable event occurs each time when a new chunk of data becomes available from the source.

Example HTML code 1:

This example illustrates the use of the onreadystatechange event:

Code

ajax.js

<head>
    <script type="text/javascript" src="ajax.js"></script>
    
    <script type="text/javascript">
        var xmlDoc = null;

        function LoadXML () {
            xmlDoc = CreateXMLDocumentObject ();    // defined in ajax.js
            if (!xmlDoc) {
                return;
            }

            var url = "large.xml";
            xmlDoc.async = true;

            if (xmlDoc.addEventListener) {  // Firefox, Opera, Google Chrome and Safari
                xmlDoc.addEventListener("load", OnLoadXML, false);
            }
            else {
                xmlDoc.onreadystatechange = OnStateChange;
            }

            xmlDoc.load (url);
        }

        function OnLoadXML () {
            LoadingFinished ();
        }

        function OnStateChange () {
            var output = document.getElementById ("output");
            switch (xmlDoc.readyState) {
            case 1:
                output.innerHTML += "The load method was called, but no data has been received yet.<br/>";
                break;
            case 2:
                output.innerHTML += "A part of the data has been loaded, but the document object model (DOM) is not yet available.<br/>";
                break;
            case 3:
                output.innerHTML += "The document object model has been built from the received data and it is available.<br/>";
                break;
            case 4:
                LoadingFinished ();
                break;
            };
        }

        function LoadingFinished () {
            var output = document.getElementById ("output");
            output.innerHTML += "All data has been loaded, the operation is finished:<br/>";

            var errorMsg = null;
            if (xmlDoc.parseError && xmlDoc.parseError.errorCode != 0) {
                errorMsg = "XML Parsing Error: <span style='color:red'>" + xmlDoc.parseError.reason
                          + " at line " + xmlDoc.parseError.line
                          + " at position " + xmlDoc.parseError.linepos
                          + "</span><br/>";
            }
            else {
                if (xmlDoc.documentElement) {
                    if (xmlDoc.documentElement.nodeName == "parsererror") {
                        errorMsg = "<span style='color:red'>" + xmlDoc.documentElement.childNodes[0].nodeValue + "</span><br/>";
                    }
                }
            }
            if (errorMsg) {
                output.innerHTML += errorMsg;
            }
            else {
                output.innerHTML += "<span style='color:blue'>The XML is valid.</span><br/>";
            }
        }
    </script>
</head>
<body>
    <button onclick="LoadXML ()">Analyze the loading process of an XML</button>
    <br/><br/>
    <div id="output" style="width:420px; height:200px; overflow:auto; border:1px solid #000000; background-color:#f5e4b1;"></div>
</body>


function CreateHTTPRequestObject () {
        // although IE supports the XMLHttpRequest object, but it does not work on local files.
    var forceActiveX = (window.ActiveXObject && location.protocol === "file:");
    if (window.XMLHttpRequest && !forceActiveX) {
        return new XMLHttpRequest();
    }
    else {
        try {
            return new ActiveXObject("Microsoft.XMLHTTP");
        } catch(e) {}
    }
    alert ("Your browser doesn't support XML handling!");
    return null;
}

function CreateMSXMLDocumentObject () {
    if (typeof (ActiveXObject) != "undefined") {
        var progIDs = [
                        "Msxml2.DOMDocument.6.0", 
                        "Msxml2.DOMDocument.5.0", 
                        "Msxml2.DOMDocument.4.0", 
                        "Msxml2.DOMDocument.3.0", 
                        "MSXML2.DOMDocument", 
                        "MSXML.DOMDocument"
                      ];
        for (var i = 0; i < progIDs.length; i++) {
            try { 
                return new ActiveXObject(progIDs[i]); 
            } catch(e) {};
        }
    }
    return null;
}

function CreateXMLDocumentObject (rootName) {
    if (!rootName) {
        rootName = "";
    }
    var xmlDoc = CreateMSXMLDocumentObject ();
    if (xmlDoc) {
        if (rootName) {
            var rootNode = xmlDoc.createElement (rootName);
            xmlDoc.appendChild (rootNode);
        }
    }
    else {
        if (document.implementation.createDocument) {
            xmlDoc = document.implementation.createDocument ("", rootName, null);
        }
    }
    
    return xmlDoc;
}

function ParseHTTPResponse (httpRequest) {
    var xmlDoc = httpRequest.responseXML;

            // if responseXML is not valid, try to create the XML document from the responseText property
    if (!xmlDoc || !xmlDoc.documentElement) {
        if (window.DOMParser) {
            var parser = new DOMParser();
            try {
                xmlDoc = parser.parseFromString (httpRequest.responseText, "text/xml");
            } catch (e) {
                alert ("XML parsing error");
                return null;
            };
        }
        else {
            xmlDoc = CreateMSXMLDocumentObject ();
            if (!xmlDoc) {
                return null;
            }
            xmlDoc.loadXML (httpRequest.responseText);

        }
    }

            // if there was an error while parsing the XML document
    var errorMsg = null;
    if (xmlDoc.parseError && xmlDoc.parseError.errorCode != 0) {
        errorMsg = "XML Parsing Error: " + xmlDoc.parseError.reason
                  + " at line " + xmlDoc.parseError.line
                  + " at position " + xmlDoc.parseError.linepos;
    }
    else {
        if (xmlDoc.documentElement) {
            if (xmlDoc.documentElement.nodeName == "parsererror") {
                errorMsg = xmlDoc.documentElement.childNodes[0].nodeValue;
            }
        }
    }
    if (errorMsg) {
        alert (errorMsg);
        return null;
    }

        // ok, the XML document is valid
    return xmlDoc;
}

    // returns whether the HTTP request was successful
function IsRequestSuccessful (httpRequest) {
        // IE: sometimes 1223 instead of 204
    var success = (httpRequest.status == 0 || 
        (httpRequest.status >= 200 && httpRequest.status < 300) || 
        httpRequest.status == 304 || httpRequest.status == 1223);
    
    return success;
}