JavaScript Advanced Programming Reading Notes (21) XML_javascript Skills in JavaScript

1. XML DOM support in IE
IE’s support for XML is based on the MSXML library of ActiveX.
1. DOM creation
For each new version of MSXML, a different XML DOM object will be created, so try to choose a new XML DOM version.
2. Loading XML
There are two types of loading XML, namely:
Loading XML string: loadXML(xml string)
Loading xml file: load (xml file path). By default, file loading is asynchronous. If you want to change it to synchronous, just change the asynce feature to true. The readyState and onreadystatechange event handlers are used when loading files asynchronously. readyState has five possible values:
0—DOM has not initialized any information;
1—DOM is loading data;
2—DOM has completed data loading;
3— —DOM is available, but some parts may not be available yet;
　4——DOM has been fully loaded and can be used.
3. Get XML
Microsoft has added xml features to each node, so it is very convenient to get XML, see the example below.
4. Explanation errors
You can use parseError to handle errors that occur during XML loading.
The parseError property is actually an object containing the following properties:
errorCode: error type numeric code, no error is 0
filePos: the location in the file where the error occurred
line: the line where the error was encountered No.
linepos: the position of the character on the line where the error was encountered
reason: an explanation for the error
srcText: the code that caused the error
url: the URL of the file that caused the error
5. Example:

Copy code The code is as follows:

function createXMLDOM(){
var arrSignatures=["MSXML2.DOMDocument.5.0","MSXML2.DOMDocument.4.0","MSXML2.DOMDocument.3.0","MSXML2.DOMDocument","Microsoft.XmlDom"];
for(var i= 0;itry{
var oXmlDom=new ActiveXObject(arrSignatures[i]);
return oXmlDom;
} catch(oError){
}
}
throw new Error("MSXML is not installed on your system");
}
var oXmlDom=createXMLDOM();
//Method 1: Load string
oXmlDom.loadXML("");
//Handling errors
if(oXmlDom.parseError != 0){
var oError=oXmlDom .parseError;
alert("An Error occurred:nError Code:" oError.errorCode
"nLine:" oError.line "nLine Pos:" oError.linepos
"nReason:" oError.reason);
} else {
var childNodes=oXmlDom.documentElement.childNodes;
console.log(childNodes.length " " childNodes[0].xml);// 1
}
//Method 2: Load XML file
oXmlDom.onreadystatechange = function(){
//Document loaded
if(oXmlDom.readyState == 4){
if(oXmlDom .parseError != 0){
var oError=oXmlDom.parseError;
alert("An Error occurred:nError Code:" oError.errorCode
"nLine:" oError.line "nLine Pos:" oError .linepos
"nReason:" oError.reason);
} else {
var childNodes=oXmlDom.documentElement.childNodes;
console.log(childNodes.length " " childNodes[0].xml );// 1
}
}
}
oXmlDom.load("test.xml");

two , XML DOM support in Mozilla
1. Create DOM
The DOM standard points out that document.implementation has a createDocument() method:
var oXmlDom=document.implementation.createDocument(""," ",null); Where, the first parameter is the namespace URL of the document, the tag name of the document element, and the document type object (always null, because it is not supported in Mozilla yet).
2. Load XML
Mozilla only supports one method of loading XML: load (file name).
Synchronous or asynchronous is determined by async, and the default is asynchronous.
If it is an XML string, use the DOMParser object to convert it to DOM. The usage is as follows:

Copy code The code is as follows:

var oParser = new DOMParser();
var oXmlDom = oParser.parseFromString("","text/xml");

The first parameter of the parseFromString method is an XML string, and the second parameter is the content type. Can be "text/xml" or "application/xml".
　3. Get XML
Since the xml features provided by Microsoft are not standard, Mozilla does not support them. Mozilla provides the XMLSerializer object:

Copy code The code is as follows:

var oSerializer = new XMLSerializer();
var sXml = oSerializer.serializeToString(oXmlDom,"text/xml"); In the following example we can see how to use the defineGetter() method to define An xml attribute.

4. Parsing error
When an error occurs during the parsing process of the XML file, XML DOM will create a document to explain the error. Regular expressions are often used to output error messages:

Copy code The code is as follows:

var reError = / >([sS]*?)Location:([sS]*?)Line Number (d ),Column (d ):([sS]*?)(?:-*^)/;
if(oXmlDom.documentElement.tagName == "parsererror"){
reError.test(oXmlDom.xml);
alert("An error occurred:nDescription: " RegExp.$1 "n"
"File: " RegExp.$2 "n"
"Line: " RegExp.$3 "n"
"Line Pos: " RegExp.$4 "n"
"Source: " RegExp.$5);
}

5. Example

Copy code The code is as follows:

var oXmlDom=document.implementation.createDocument("","",null);
oXmlDom.async = false;
oXmlDom.onload = function(){
alert( 'Done');
}
var reError = />([sS]*?)Location:([sS]*?)Line Number (d ),Column (d ):( [sS]*?)(?:-*^)/;
if(oXmlDom.documentElement.tagName == "parsererror"){
reError.test(oXmlDom.xml);
alert(" An error occurred:nDescription: " RegExp.$1 "n"
"File: " RegExp.$2 "n"
"Line: " RegExp.$3 "n"
"Line Pos: " RegExp.$4 "n"
"Source: " RegExp.$5);
}
Node.prototype.__defineGetter__("xml", function () {
var oSerializer = new XMLSerializer();
return oSerializer.serializeToString(this, "text/xml");
});
oXmlDom.load('test.xml');
alert(oXmldom.xml);
var oNode = oXmlDom.documentElement.childNodes[1];
alert(oNode.xml);

3. General interface
The following is a general interface compatible with IE and FireFox :

Copy code The code is as follows:

function XmlDom() {
if (window.ActiveXObject) {//IE
var arrSignatures = ["MSXML2.DOMDocument.5.0", "MSXML2.DOMDocument.4.0",
"MSXML2.DOMDocument.3.0", "MSXML2.DOMDocument", "Microsoft.XmlDom"];
for (var i = 0; i < arrSignatures.length; i ) {
try {
var oXmlDom = new ActiveXObject(arrSignatures[i]);
return oXmlDom;
}
catch (oError) {
//ignore
}
}
throw new Error("MSXML is not installed on your system.");
} else if (document.implementation && document.implementation.createDocument) {
var oXmlDom = document.implementation.createDocument("", "", null);
oXmlDom.parseError = {valueOf:function () {
return this.errorCode;
}, toString:function () {
return this.errorCode.toString();
}};
oXmlDom.__initError__();
oXmlDom.addEventListener("load", function () {
this.__checkForErrors__();
this.__changeReadyState__(4);
}, false);
return oXmlDom;
} else {
throw new Error("Your browser doesn't support an XML DOM object.");
}
}
if (isMoz) {
Document.prototype._readyState_ = 0;
Document.prototype.onreadystatechange = null;
Document.prototype.__changeReadyState__ = function (iReadyState) {
this._readyState_ = iReadyState;
if (typeof this.onreadystatechange == "function") {
this.onreadystatechange();
}
};
Document.prototype.__initError__ = function () {
this.parseError.errorCode = 0;
this.parseError.filepos = -1;
this.parseError.line = -1;
this.parseError.linepos = -1;
this.parseError.reason = null;
this.parseError.srcText = null;
this.parseError.url = null;
};
Document.prototype.__checkForErrors__ = function () {
if (this.documentElement.tagName == "parsererror") {
var reError = />([sS]*?)Location:([sS]*?)Line Number (d ),Column (d ):([sS]*?)(?:-*^)/;
reError.test(this.xml);
this.parseError.errorCode = -999999;
this.parseError.reason = RegExp.$1;
this.parseError.url = RegExp.$2;
this.parseError.line = parseInt(RegExp.$3);
this.parseError.linepos = parseInt(RegExp.$4);
this.parseError.srcText = RegExp.$5;
}
};
Document.prototype.loadXML = function (sXml) {
this.__initError__();
this.__changeReadyState__(1);
var oParser = new DOMParser();
var oXmlDom = oParser.parseFromString(sXml, "text/xml");
while (this.firstChild) {
this.removeChild(this.firstChild);
}
for (var i = 0; i < oXmlDom.childNodes.length; i ) {
var oNewNode = this.importNode(oXmlDom.childNodes[i], true);
this.appendChild(oNewNode);
}
this.__checkForErrors__();
this.__changeReadyState__(4);
};
Document.prototype.__load__ = Document.prototype.load;
Document.prototype.load = function (sURL) {
this.__initError__();
this.__changeReadyState__(1);
this.__load__(sURL);
};
Document.prototype.getReadyState = function () {
return this._readyState_;
};
Node.prototype.__defineGetter__("xml", function () {
var oSerializer = new XMLSerializer();
return oSerializer.serializeToString(this, "text/xml");
});
}

四、其他浏览器
　　本书中没有讲到其他浏览器，如现在很火的Chrome，最新版的主流浏览器现在都已支持上面讲到的Mozilla方式。如果不支持，可以用AJAX来读取处理XML。
作者：Artwl
出处：http://artwl.cnblogs.com