getElementsByTagName vs selectNodes效率 及兼容的selectNodes实现

时间：2021-05-28

于是就测试了下：
复制代码 代码如下:
var stringToDom=function(text) {
var doc;
if(window.ActiveXObject) {
doc = new ActiveXObject("MSXML2.DOMDocument");
doc.loadXML(text).documentElement;
} else {
doc = (new DOMParser()).parseFromString(text,"text/xml");
}
return doc;
}
var xmlDoc=stringToDom("<body><a href='a'>a</a><a href='b'>b</a></body>"),
c,
d1=new Date();
for(var i=0;i<100000;i++){
c=xmlDoc.getElementsByTagName("a");
}
document.write("getElementsByTagName: ",new Date()-d1);
d1=new Date();
try{
for(var i=0;i<100000;i++){
c=xmlDoc.selectNodes("a");
}
document.write("<br/>selectNodes: ",new Date()-d1);
}catch(ex){document.write("<br/>error:"+ex)}

在IE下selectNodes还是快多了，
可以FF下却没有这个方法，google了下，找了方法，使用XPathEvaluator来实现，下面是具体实现，不过效率就不太理想了：
复制代码 代码如下:
if (!window.ActiveXObject) {
(function(){
var oEvaluator=new XPathEvaluator(),oResult;
XMLDocument.prototype.selectNodes = function(sXPath) {
oResult = oEvaluator.evaluate(sXPath, this, null, XPathResult.ORDERED_NODE_ITERATOR_TYPE, null);
var aNodes = [];
if (oResult != null) {
var oElement = oResult.iterateNext();
while (oElement) {
aNodes[aNodes.length]=oElement;
oElement = oResult.iterateNext();
}
}
return aNodes;
}
})()
}

evaluate(xpathExpression, contextNode, namespaceResolver, resultType, result);
Returns an XPathResult based on an XPath expression and other given parameters.
xpathExpression is a string representing the XPath to be evaluated.
contextNode specifies the context node for the query (see the [http:///sohighthesky
*content: selectNodes vs getElementsByTagName
*/
if (!window.ActiveXObject) {
(function(){
var oEvaluator=new XPathEvaluator(),oResult;
XMLDocument.prototype.selectNodes = function(sXPath) {
oResult = oEvaluator.evaluate(sXPath, this, null, XPathResult.ORDERED_NODE_ITERATOR_TYPE, null);
var aNodes = [];
if (oResult != null) {
var oElement = oResult.iterateNext();
while (oElement) {
aNodes[aNodes.length]=oElement;
oElement = oResult.iterateNext();
}
}
return aNodes;
}
XMLDocument.prototype.selectSingleNode = function(sXPath) {
oResult = oEvaluator.evaluate(sXPath, this, null, XPathResult.FIRST_ORDERED_NODE_TYPE, null);
// FIRST_ORDERED_NODE_TYPE returns the first match to the xpath.
return oResult==null?null:oResult.singleNodeValue;
}
})()
}
var stringToDom=function(text) {
var doc;
if(window.ActiveXObject) {
doc = new ActiveXObject("MSXML2.DOMDocument");
doc.loadXML(text).documentElement;
} else {
doc = (new DOMParser()).parseFromString(text,"text/xml");
}
return doc;
}
var xmlDoc=stringToDom("<body><a href='a'>a</a><a href='b'>b</a></body>"),
c,
d1=new Date();
for(var i=0;i<100000;i++){
c=xmlDoc.getElementsByTagName("a");
}
document.write("getElementsByTagName: ",new Date()-d1);
d1=new Date();
try{
for(var i=0;i<100000;i++){
c=xmlDoc.selectNodes("a");
}
document.write("<br/>selectNodes: ",new Date()-d1);
}catch(ex){document.write("<br/>error:"+ex)}

</script>
</html>

声明：本页内容来源网络，仅供用户参考；我单位不保证亦不表示资料全面及准确无误，也不保证亦不表示这些资料为最新信息，如因任何原因，本网内容或者用户因倚赖本网内容造成任何损失或损害，我单位将不会负任何法律责任。如涉及版权问题，请提交至online#300.cn邮箱联系删除。

相关文章