jQuery源码分析之sizzle选择器详解

jQuery.find = Sizzle;
function Sizzle(selector, context, results, seed) {
 var m, i, elem, nid, match, groups, newSelector, newContext = context && context.ownerDocument,
 // nodeType defaults to 9, since context defaults to document
 nodeType = context ? context.nodeType : 9;
 results = results || [];
 // Return early from calls with invalid selector or context
 if (typeof selector !== "string" || !selector || nodeType !== 1 && nodeType !== 9 && nodeType !== 11) {
 return results;
 }
 // Try to shortcut find operations (as opposed to filters) in HTML documents
 if (!seed) {
 if ((context ? context.ownerDocument || context : preferredDoc) !== document) {
  // setDocument 函数其实是用来将 context 设置成 document，考虑到浏览器的兼容性
  setDocument(context);
 }
 context = context || document;
 // true
 if (documentIsHTML) {
  // match 就是那个有规律的数组
  if (nodeType !== 11 && (match = rquickExpr.exec(selector))) {
  // selector 是 id 的情况
  if ((m = match[1])) {
   // Document context
   if (nodeType === 9) {
   if ((elem = context.getElementById(m))) {
    if (elem.id === m) {
     results.push(elem);
     return results;
    }
   } else {
    return results;
   }
   // 非 document 的情况
   } else {
   if (newContext && (elem = newContext.getElementById(m)) && contains(context, elem) && elem.id === m) {
    results.push(elem);
    return results;
   }
   }
  // selector 是 tagName 情况
  } else if (match[2]) {
   // 这里的 push：var push = arr.push
   push.apply(results, context.getElementsByTagName(selector));
   return results;
  // selector 是 class 情况
  } else if ((m = match[3]) && support.getElementsByClassName && context.getElementsByClassName) {
   push.apply(results, context.getElementsByClassName(m));
   return results;
  }
  }
  // 如果浏览器支持 querySelectorAll
  if (support.qsa && !compilerCache[selector + " "] && (!rbuggyQSA || !rbuggyQSA.test(selector))) {
  if (nodeType !== 1) {
   newContext = context;
   newSelector = selector;
   // qSA looks outside Element context, which is not what we want
   // Support: IE <=8,还是要考虑兼容性
  } else if (context.nodeName.toLowerCase() !== "object") {
   // Capture the context ID, setting it first if necessary
   if ((nid = context.getAttribute("id"))) {
   nid = nid.replace(rcssescape, fcssescape);
   } else {
   context.setAttribute("id", (nid = expando));
   }
   // Sizzle 词法分析的部分
   groups = tokenize(selector);
   i = groups.length;
   while (i--) {
   groups[i] = "#" + nid + " " + toSelector(groups[i]);								 
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