用Javascript解析html

逗咳嗽 2015-12-13

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说到用Javascript解析html，大家肯定会想到dom或者正则表达式，但这两个都不是我今天我要说的。dom很不错，不过效率不高，而且必须将要解析的html插入到当前页面或者建立一个iframe才能进行，而用正则表达式，又有太过繁琐和难以维护的问题。

有人要说了，ruby、php、python有了那么多开源的优秀的html解析的类库，什么beautiful soap，什么Mechanize，什么Hpricot，什么ScRUBYt，你为什么非要自讨苦吃用javascript来干这活呢？

答案是：如果只允许你用javascript和html开发程序呢，比如开发adobe air的程序，比如下一步我要做的基于基于内嵌webkit组件的Android应用快速开发框架，有时候，轮子还是得自己造的。

我的这个解析实现只是雏形，它以Erik Arvidsson开发的SimpleHtmlParser 作为html的分析器。SimpleHtmlParser是一个基于Sax模型实现的html分析器，他能分析非标准的xml的格式的html别把转换作为一个标准的xml处理。有了这个解析器做基础，我写了个简单的html_extractor，用来分析html并获取指定标记内的内容。

html_extractor的使用

new html_extractor(html): 指定html字符串创建一个html_extractor对象

方法：

tag(tagName):设定一个待匹配的元素名，返回结果为当面的html_extractor对象

attr(attrName, attrValue):设定匹配的属性条件，attr必须在tag后，返回结果为当面的html_extractor对象

match(innerOrNot):执行匹配，返回结果为符合条件的字符串数组。

示例：

Js代码

html = "<div>div1</div>";
//取出div标记下的内容，ret的结果是["div1"]
var ret = new html_extractor(html).tag("div").match();
html = "<div id=\"head\">head</div><div id=\"content\"><p><ul><li>item1</li><li>item2</li></ul></div>";
//取出属性id=content的div下的所有li下的内容，返回结果将是["item1", "item2"]
ret = new html_extractor(html).tag("div").attr("id", "content").tag("li").match();
//提取baidu搜索结果
ret = new html_extractor(html).tag("td").attr("class", "f").match();
//提取google搜索结果
ret = new html_extractor(html).tag("li").attr("class", "g").match();

源代码(当前代码还非常原始，进攻参考，请慎重使用)

Js代码

var html_extractor = function(html)
{
this.parser = new SimpleHtmlParser;
this.html = html;
this.tags = [];
this.attrs = [];
}
html_extractor.prototype.tag = function(tag)
{
this.tags.push(tag.toLowerCase());
return this;
}
html_extractor.prototype.attr = function(name, value)
{
var len = this.tags.length - 1;
if (this.attrs[len] == undefined)this.attrs[len] = [];
this.attrs[len].push({name:name.toLowerCase(), value: value});
return this;
}
html_extractor.prototype.match = function(inner)
{
var self = this;
var handler = function(){
this._tag_index = 0;
this._matched_tags = [];
this._matched = [];
this._result = "";
this.result = [];
this._all_matched = false;
for( var i = 0; i < self.tags.length; i++)this._matched[i] = false;
this.inner = true;
if (inner != undefined && inner != null)
{
this.inner = inner;
}
};
handler.prototype = {
startElement: function (tag, attrs) {
this.tag_index++;
tag = tag.toLowerCase();
//air.trace("process tag:" + tag + " " + this.tag_index);
if (this._all_matched )
{
this._result += get_start_tag(tag, attrs);
return;
}
for( var i = 0; i < this._matched.length; i++)
{
//air.trace(i + ":" + this._matched[i]);
if (!this._matched[i] )
{
if (self.tags[i] == tag)
{
this._matched[i] = true;
if (self.attrs[i] != undefined)
{
for(var n = 0; n < self.attrs[i].length; n++)
{
var attr = self.attrs[i][n];
if (attr != undefined)
{
if(attrs[attr.name] != attr.value) this._matched[i] = false;
};
}
}
if (this._matched[i] )
{
//todo callback
//air.trace(i + ":" + this._matched[i] + " first");
this._matched_tags[this.tag_index] = i;
if (i == self.tags.length -1)
{
this._all_matched = true;
if (!this.inner) this._result += get_start_tag(tag, attrs);
}
return;
}
}
if (!this._matched[i] ){break;}
}
}
},
endElement: function (tag) {
tag = tag.toLowerCase();
if (this._matched_tags[this.tag_index] != undefined)
{
this._matched[this._matched_tags[this.tag_index]] = false;
if (this._all_matched)
{
if (!this.inner)this._result += "</" + tag +">";
this.result.push(this._result);
this._result = "";
this._all_matched = false;
}
}
else if (this._all_matched)
{
this._result += "</" + tag +">";
}
//air.trace("finished tag:" + tag + " " + this.tag_index);
this.tag_index--;
},
characters: function (s) { if(this._all_matched)this._result += s;},
comment: function (s) {}
};
this.parser.contentHandler = new handler;
this.parser.parse(this.html);
//reset
this.tags = [];
this.attrs = [];
return this.parser.contentHandler.result;
}
function get_start_tag(tag, attrs)
{
var ret = "<" + tag;
for (var key in attrs)
{
value = attrs[key];
ret += " " + key + "=\"" + value + "\"";
}
ret += ">";
return ret;
}
/** SimpleHtmlParser
* Original code by Erik Arvidsson, Mozilla Public License
* http://erik./simplehtmlparser/simplehtmlparser.js
*/
/*
var handler ={
startElement: function (sTagName, oAttrs) {},
endElement: function (sTagName) {},
characters: function (s) {},
comment: function (s) {}
};
*/
function SimpleHtmlParser()
{
}
SimpleHtmlParser.prototype = {
handler: null,
// regexps
startTagRe: /^<([^>\s\/]+)((\s+[^=>\s]+(\s*=\s*((\"[^"]*\")|(\'[^']*\')|[^>\s]+))?)*)\s*\/?\s*>/m,
endTagRe: /^<\/([^>\s]+)[^>]*>/m,
attrRe: /([^=\s]+)(\s*=\s*((\"([^"]*)\")|(\'([^']*)\')|[^>\s]+))?/gm,
parse: function (s, oHandler)
{
if (oHandler)
this.contentHandler = oHandler;
var i = 0;
var res, lc, lm, rc, index;
var treatAsChars = false;
var oThis = this;
while (s.length > 0)
{
// Comment
if (s.substring(0, 4) == "<!--")
{
index = s.indexOf("-->");
if (index != -1)
{
this.contentHandler.comment(s.substring(4, index));
s = s.substring(index + 3);
treatAsChars = false;
}
else
{
treatAsChars = true;
}
}
// end tag
else if (s.substring(0, 2) == "</")
{
if (this.endTagRe.test(s))
{
lc = RegExp.leftContext;
lm = RegExp.lastMatch;
rc = RegExp.rightContext;
lm.replace(this.endTagRe, function ()
{
return oThis.parseEndTag.apply(oThis, arguments);
});
s = rc;
treatAsChars = false;
}
else
{
treatAsChars = true;
}
}
// start tag
else if (s.charAt(0) == "<")
{
if (this.startTagRe.test(s))
{
lc = RegExp.leftContext;
lm = RegExp.lastMatch;
rc = RegExp.rightContext;
lm.replace(this.startTagRe, function ()
{
return oThis.parseStartTag.apply(oThis, arguments);
});
s = rc;
treatAsChars = false;
}
else
{
treatAsChars = true;
}
}
if (treatAsChars)
{
index = s.indexOf("<");
if (index == -1)
{
this.contentHandler.characters(s);
s = "";
}
else
{
this.contentHandler.characters(s.substring(0, index));
s = s.substring(index);
}
}
treatAsChars = true;
}
},
parseStartTag: function (sTag, sTagName, sRest)
{
var attrs = this.parseAttributes(sTagName, sRest);
this.contentHandler.startElement(sTagName, attrs);
},
parseEndTag: function (sTag, sTagName)
{
this.contentHandler.endElement(sTagName);
},
parseAttributes: function (sTagName, s)
{
var oThis = this;
var attrs = {};
s.replace(this.attrRe, function (a0, a1, a2, a3, a4, a5, a6)
{
//attrs.push(oThis.parseAttribute(sTagName, a0, a1, a2, a3, a4, a5, a6));
attr = oThis.parseAttribute(sTagName, a0, a1, a2, a3, a4, a5, a6);
attrs[attr.name] = attr.value;
});
return attrs;
},
parseAttribute: function (sTagName, sAttribute, sName)
{
var value = "";
if (arguments[7])
value = arguments[8];
else if (arguments[5])
value = arguments[6];
else if (arguments[3])
value = arguments[4];
var empty = !value && !arguments[3];
return {name: sName.toLowerCase(), value: empty ? null : value};
}
};