jQuery源码学习笔记六

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hasClassName
					if ( 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 negative
				match[2] = (test[1] + (test[2] || 1)) - 0;
				match[3] = test[3] - 0;
			}

			// TODO: Move to normal caching system
			match[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 one
				if ( 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 properly
			elem.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,h6
			return /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;
	};
}