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今天我开始攻略jQuery的心脏，css选择器。不过Sizzle是如此复杂的东西，我发现不能跟着John Resig的思路一行行读下去，因此下面的代码和jQuery的次序是不一样的。

jQuery的代码是包含在一个巨大的闭包中，Sizzle又在它里面开辟另一个闭包。它是完全独立于jQuery，jQuery通过find方法来调用Sizzle。一开始是这几个变量，尤其是那个正则，用于分解我们传入的字符串

var chunker = /((?:\((?:\([^()]+\)|[^()]+)+\)|\[(?:\[[^[\]]*\]|['"][^'"]*['"]|[^[\]'"]+)+\]|\\.|[^ >+~,(\[\\]+)+|[>+~])(\s*,\s*)?/g,done = 0,toString = Object.prototype.toString;

然后我们看其表达式，用于深加工与过滤以及简单的查找：

//@author  司徒正美|なさみ|cheng http://www.cnblogs.com/rubylouvre/ All rights reserved
var Expr = Sizzle.selectors = {order: [ "ID", "NAME", "TAG" ],match: {ID: /#((?:[\w\u00c0-\uFFFF_-]|\\.)+)/,CLASS: /\.((?:[\w\u00c0-\uFFFF_-]|\\.)+)/,NAME: /\[name=['"]*((?:[\w\u00c0-\uFFFF_-]|\\.)+)['"]*\]/,ATTR: /\[\s*((?:[\w\u00c0-\uFFFF_-]|\\.)+)\s*(?:(\S?=)\s*(['"]*)(.*?)\3|)\s*\]/,TAG: /^((?:[\w\u00c0-\uFFFF\*_-]|\\.)+)/,CHILD: /:(only|nth|last|first)-child(?:\((even|odd|[\dn+-]*)\))?/,POS: /:(nth|eq|gt|lt|first|last|even|odd)(?:\((\d*)\))?(?=[^-]|$)/,PSEUDO: /:((?:[\w\u00c0-\uFFFF_-]|\\.)+)(?:\((['"]*)((?:\([^\)]+\)|[^\2\(\)]*)+)\2\))?/},attrMap: {//一些属性不能直接其HTML名字去取，需要用其在javascript的属性名"class": "className","for": "htmlFor"},attrHandle: {href: function(elem){return elem.getAttribute("href");}},relative: {//相邻选择符"+": function(checkSet, part, isXML){var isPartStr = typeof part === "string",isTag = isPartStr && !/\W/.test(part),isPartStrNotTag = isPartStr && !isTag;if ( isTag && !isXML ) {part = part.toUpperCase();}for ( var i = 0, l = checkSet.length, elem; i < l; i++ ) {if ( (elem = checkSet[i]) ) {while ( (elem = elem.previousSibling) && elem.nodeType !== 1 ) {}checkSet[i] = isPartStrNotTag || elem && elem.nodeName === part ?elem || false :elem === part;}}if ( isPartStrNotTag ) {Sizzle.filter( part, checkSet, true );}},//亲子选择符">": function(checkSet, part, isXML){var isPartStr = typeof part === "string";if ( isPartStr && !/\W/.test(part) ) {part = isXML ? part : part.toUpperCase();for ( var i = 0, l = checkSet.length; i < l; i++ ) {var elem = checkSet[i];if ( elem ) {var parent = elem.parentNode;checkSet[i] = parent.nodeName === part ? parent : false;}}} else {for ( var i = 0, l = checkSet.length; i < l; i++ ) {var elem = checkSet[i];if ( elem ) {checkSet[i] = isPartStr ?elem.parentNode :elem.parentNode === part;}}if ( isPartStr ) {Sizzle.filter( part, checkSet, true );}}},//后代选择符"": function(checkSet, part, isXML){var doneName = done++, checkFn = dirCheck;if ( !part.match(/\W/) ) {var nodeCheck = part = isXML ? part : part.toUpperCase();checkFn = dirNodeCheck;}checkFn("parentNode", part, doneName, checkSet, nodeCheck, isXML);},//兄长选择符"~": function(checkSet, part, isXML){var doneName = done++, checkFn = dirCheck;if ( typeof part === "string" && !part.match(/\W/) ) {var nodeCheck = part = isXML ? part : part.toUpperCase();checkFn = dirNodeCheck;}checkFn("previousSibling", part, doneName, checkSet, nodeCheck, isXML);}},find: {ID: function(match, context, isXML){if ( typeof context.getElementById !== "undefined" && !isXML ) {var m = context.getElementById(match[1]);return m ? [m] : [];//就算只有一个也放进数组}},NAME: function(match, context, isXML){if ( typeof context.getElementsByName !== "undefined" ) {var ret = [], results = context.getElementsByName(match[1]);for ( var i = 0, l = results.length; i < l; i++ ) {if ( results[i].getAttribute("name") === match[1] ) {ret.push( results[i] );}}return ret.length === 0 ? null : ret;}},TAG: function(match, context){return context.getElementsByTagName(match[1]);}},preFilter: {//这里，如果符合的话都返回字符串CLASS: function(match, curLoop, inplace, result, not, isXML){match = " " + match[1].replace(/\\/g, "") + " ";if ( isXML ) {return match;}for ( var i = 0, elem; (elem = curLoop[i]) != null; i++ ) {if ( elem ) {//相当于hasClassNameif ( not ^ (elem.className && (" " + elem.className + " ").indexOf(match) >= 0) ) {if ( !inplace )result.push( elem );} else if ( inplace ) {curLoop[i] = false;}}}return false;},ID: function(match){return match[1].replace(/\\/g, "");},TAG: function(match, curLoop){for ( var i = 0; curLoop[i] === false; i++ ){}return curLoop[i] && isXML(curLoop[i]) ? match[1] : match[1].toUpperCase();},CHILD: function(match){//把nth(****)里面的表达式都弄成an+b的样子if ( match[1] == "nth" ) {// parse equations like 'even', 'odd', '5', '2n', '3n+2', '4n-1', '-n+6'var test = /(-?)(\d*)n((?:\+|-)?\d*)/.exec(match[2] == "even" && "2n" || match[2] == "odd" && "2n+1" ||!/\D/.test( match[2] ) && "0n+" + match[2] || match[2]);// calculate the numbers (first)n+(last) including if they are negativematch[2] = (test[1] + (test[2] || 1)) - 0;match[3] = test[3] - 0;}// TODO: Move to normal caching systemmatch[0] = done++;return match;},ATTR: function(match, curLoop, inplace, result, not, isXML){var name = match[1].replace(/\\/g, "");if ( !isXML && Expr.attrMap[name] ) {match[1] = Expr.attrMap[name];}if ( match[2] === "~=" ) {match[4] = " " + match[4] + " ";}return match;},PSEUDO: function(match, curLoop, inplace, result, not){if ( match[1] === "not" ) {// If we're dealing with a complex expression, or a simple oneif ( match[3].match(chunker).length > 1 || /^\w/.test(match[3]) ) {match[3] = Sizzle(match[3], null, null, curLoop);} else {var ret = Sizzle.filter(match[3], curLoop, inplace, true ^ not);if ( !inplace ) {result.push.apply( result, ret );}return false;}} else if ( Expr.match.POS.test( match[0] ) || Expr.match.CHILD.test( match[0] ) ) {return true;}return match;},POS: function(match){match.unshift( true );return match;}},filters: {//都是返回布尔值enabled: function(elem){//不能为隐藏域return elem.disabled === false && elem.type !== "hidden";},disabled: function(elem){return elem.disabled === true;},checked: function(elem){return elem.checked === true;},selected: function(elem){// Accessing this property makes selected-by-default// options in Safari work properlyelem.parentNode.selectedIndex;return elem.selected === true;},parent: function(elem){//是否是父节点（是，肯定有第一个子节点）return !!elem.firstChild;},empty: function(elem){//是否为空，一点节点也没有return !elem.firstChild;},has: function(elem, i, match){return !!Sizzle( match[3], elem ).length;},header: function(elem){//是否是h1,h2,h3,h4,h5,h6return /h\d/i.test( elem.nodeName );},text: function(elem){//文本域，下面几个相仿，基本上可以归类于属性选择器return "text" === elem.type;},radio: function(elem){return "radio" === elem.type;},checkbox: function(elem){return "checkbox" === elem.type;},file: function(elem){return "file" === elem.type;},password: function(elem){return "password" === elem.type;},submit: function(elem){return "submit" === elem.type;},image: function(elem){return "image" === elem.type;},reset: function(elem){return "reset" === elem.type;},button: function(elem){return "button" === elem.type || elem.nodeName.toUpperCase() === "BUTTON";},input: function(elem){return /input|select|textarea|button/i.test(elem.nodeName);}},setFilters: {//子元素过滤器first: function(elem, i){return i === 0;},last: function(elem, i, match, array){return i === array.length - 1;},even: function(elem, i){return i % 2 === 0;},odd: function(elem, i){return i % 2 === 1;},lt: function(elem, i, match){return i < match[3] - 0;},gt: function(elem, i, match){return i > match[3] - 0;},nth: function(elem, i, match){return match[3] - 0 == i;},eq: function(elem, i, match){return match[3] - 0 == i;}},filter: {PSEUDO: function(elem, match, i, array){var name = match[1], filter = Expr.filters[ name ];if ( filter ) {return filter( elem, i, match, array );} else if ( name === "contains" ) {return (elem.textContent || elem.innerText || "").indexOf(match[3]) >= 0;} else if ( name === "not" ) {var not = match[3];for ( var i = 0, l = not.length; i < l; i++ ) {if ( not[i] === elem ) {return false;}}return true;}},CHILD: function(elem, match){var type = match[1], node = elem;switch (type) {case 'only':case 'first':while (node = node.previousSibling)  {if ( node.nodeType === 1 ) return false;}if ( type == 'first') return true;node = elem;case 'last':while (node = node.nextSibling)  {if ( node.nodeType === 1 ) return false;}return true;case 'nth':var first = match[2], last = match[3];if ( first == 1 && last == 0 ) {return true;}var doneName = match[0],parent = elem.parentNode;if ( parent && (parent.sizcache !== doneName || !elem.nodeIndex) ) {var count = 0;for ( node = parent.firstChild; node; node = node.nextSibling ) {if ( node.nodeType === 1 ) {node.nodeIndex = ++count;//添加一个私有属性}} parent.sizcache = doneName;}var diff = elem.nodeIndex - last;if ( first == 0 ) {return diff == 0;//判断是否为第一个子元素} else {return ( diff % first == 0 && diff / first >= 0 );}}},ID: function(elem, match){return elem.nodeType === 1 && elem.getAttribute("id") === match;},TAG: function(elem, match){return (match === "*" && elem.nodeType === 1) || elem.nodeName === match;},CLASS: function(elem, match){return (" " + (elem.className || elem.getAttribute("class")) + " ").indexOf( match ) > -1;},ATTR: function(elem, match){var name = match[1],result = Expr.attrHandle[ name ] ?Expr.attrHandle[ name ]( elem ) :elem[ name ] != null ?elem[ name ] :elem.getAttribute( name ),value = result + "",type = match[2],check = match[4];return result == null ?type === "!=" :type === "=" ?value === check :type === "*=" ?value.indexOf(check) >= 0 :type === "~=" ?(" " + value + " ").indexOf(check) >= 0 :!check ?value && result !== false :type === "!=" ?value != check :type === "^=" ?value.indexOf(check) === 0 :type === "$=" ?value.substr(value.length - check.length) === check :type === "|=" ?value === check || value.substr(0, check.length + 1) === check + "-" :false;},POS: function(elem, match, i, array){var name = match[2], filter = Expr.setFilters[ name ];if ( filter ) {return filter( elem, i, match, array );}}}
};var origPOS = Expr.match.POS;

但上图没有完全显现Sizzle复杂的工作机制，它是从左到右工作，加工了一个字符串，查找，然后过滤非元素节点，再跟据其属性或内容或在父元素的顺序过滤，然后到下一个字符串，这时搜索起点就是上次的结果数组的元素节点，想象一下草根的样子吧。在许多情况下，选择器都是靠工作的，element.getElementsByTagName(*)，获得其一元素的所有子孙，因此Expr中的过滤器特别多。为了过快查找速度，如有些浏览器已经实现了getElementsByClassName，jQuery也设法把它们利用起来。

for ( var type in Expr.match ) {//重写Expr.match中的正则，利用负向零宽断言让其更加严谨Expr.match[ type ] = RegExp( Expr.match[ type ].source + /(?![^\[]*\])(?![^\(]*\))/.source );
}

接着下来我们还是未到时候看上面的主程序，继续看它的辅助方法。

//把NodeList HTMLCollection转换成纯数组，如果有第二参数（上次查找的结果），则把它们加入到结果集中
var makeArray = function(array, results) {array = Array.prototype.slice.call( array );if ( results ) {results.push.apply( results, array );return results;}return array;
};try {//基本上是用于测试IE的，IE的NodeList HTMLCollection不支持用数组的slice转换为数组Array.prototype.slice.call( document.documentElement.childNodes );//这时就要重载makeArray，一个个元素搬入一个空数组中了
} catch(e){makeArray = function(array, results) {var ret = results || [];if ( toString.call(array) === "[object Array]" ) {Array.prototype.push.apply( ret, array );} else {if ( typeof array.length === "number" ) {for ( var i = 0, l = array.length; i < l; i++ ) {ret.push( array[i] );}} else {for ( var i = 0; array[i]; i++ ) {ret.push( array[i] );}}}return ret;};
}