jQuery选择器源码解读（一）：Sizzle方法

对jQuery的Sizzle各方法做了深入分析（同时也参考了一些网上资料）后，将结果分享给大家。我将采用连载的方式，对Sizzle使用的一些方法详细解释一下，每篇文章介绍一个方法。

若需要转载，请写明出处，多谢。

function Sizzle(selector, context, results, seed) {
	var match, elem, m, nodeType,
	// QSA vars
	i, groups, old, nid, newContext, newSelector;

	
	if ((context ? context.ownerdocument || context : preferredDoc) !== document) {
		setdocument(context);
	}

	context = context || document;
	results = results || [];

	
	if (!selector || typeof selector !== "string") {
		return results;
	}

	
	if ((nodeType = context.nodeType) !== 1 && nodeType !== 9) {
		return [];
	}

	// 若当前过滤的是HTML文档，且没有设定seed，则执行if内的语句体
	if (documentIsHTML && !seed) {

		
		if ((match = rquickExpr.exec(selector))) {
			// Speed-up: Sizzle("#ID")
			// 处理ID类型选择器，如：#ID
			if ((m = match[1])) {
				// 若当前上下文是一个document，则执行if内语句体
				if (nodeType === 9) {
					elem = context.getElementById(m);
					// Check parentNode to catch when Blackberry 4.6
					// returns
					// nodes that are no longer in the document #6963
					if (elem && elem.parentNode) {
						// Handle the case where IE, Opera, and Webkit
						// return items
						// by name instead of ID
						 
						if (elem.id === m) {
							results.push(elem);
							return results;
						}
					} else {
						return results;
					}
				} else {
					// Context is not a document
					
					if (context.ownerdocument
							&& (elem = context.ownerdocument.getElementById(m))
							&& contains(context, elem) && elem.id === m) {
						results.push(elem);
						return results;
					}
				}

				// Speed-up: Sizzle("TAG")
				// 处理Tag类型选择器，如：SPAN
			} else if (match[2]) {
				push.apply(results, context.getElementsByTagName(selector));
				return results;

				// Speed-up: Sizzle(".CLASS")
				 
				
			} else if ((m = match[3]) && support.getElementsByClassName
					&& context.getElementsByClassName) {
				push.apply(results, context.getElementsByClassName(m));
				return results;
			}
		}

		// QSA path
		
		
		if (support.qsa && (!rbuggyQSA || !rbuggyQSA.test(selector))) {
			nid = old = expando;
			newContext = context;
			// 若context是document，则newSelector取自selector，否则为false
			newSelector = nodeType === 9 && selector;

			// qSA works strangely on Element-rooted queries
			// We can work around this by specifying an extra ID on the
			// root
			// and working up from there (Thanks to Andrew Dupont for
			// the technique)
			// IE 8 doesn't work on object elements
			if (nodeType === 1 && context.nodeName.toLowerCase() !== "object") {
				groups = tokenize(selector);

				if ((old = context.getAttribute("id"))) {
					
					nid = old.replace(rescape, "\$&");
				} else {
					context.setAttribute("id", nid);
				}
				nid = "[id='" + nid + "'] ";

				// 重新组合新的选择器
				i = groups.length;
				while (i--) {
					groups[i] = nid + toSelector(groups[i]);
				}
				
				newContext = rsibling.test(selector) && context.parentNode
						|| context;
				newSelector = groups.join(",");
			}

			if (newSelector) {
				
				try {
					// 将querySelectorAll获取的结果并入results，而后返回resulsts
					push.apply(results, newContext
							.querySelectorAll(newSelector));
					return results;
				} catch (qsaError) {
				} finally {
					if (!old) {
						context.removeAttribute("id");
					}
				}
			}
		}
	}

	// All others
	// 除上述快捷方式和调用querySelectorAll方式直接获取结果外，其余都需调用select来获取结果
	
	return select(selector.replace(rtrim, "$1"), context, results, seed);
}

各位朋友，若觉得写得不错，帮我顶一下，给点动力，多谢！