jQuery1.11源码分析(5)-----Sizzle编译和过滤阶段[原创]

在上一章中，我们说到在之前的查找阶段我们已经获得了待选集seed，那么这一章我们就来讲如何将seed待选集过滤，以获得我们最终要用的元素。

其实思路本质上还是不停地根据token过滤，但compile这个函数将这些matcher（filter生成的闭包过滤函数）给编译成一个函数(这个效率和我们直接使用过滤函数差不多，关键是在后面)，再保存这一个函数，以后遇到同样的selector就可以不用再编译，直接调用就可以了。

接下来我们看看compile的代码

compile = Sizzle.compile = function( selector, group /* Internal Use Only */ ) {
    console.log('compile begin');
    console.log('arguments:selector, group');
    console.log(arguments);
	var i,
		setMatchers = [],
		elementMatchers = [],
		cached = compilerCache[ selector + " " ];

	if ( !cached ) {
		// Generate a function of recursive functions that can be used to check each element
		if ( !group ) {
			group = tokenize( selector );
		}
		i = group.length;
		while ( i-- ) {
            console.log('compile matcherFromTokens '+i);
			cached = matcherFromTokens( group[i] );
            console.log('compile after matcherFromTokens '+i);
            console.log([cached]);
			if ( cached[ expando ] ) {
                //这里的区别是，setMatchers是当有伪类进行过递归调用Sizzle时出现的多层次的matcher
				setMatchers.push( cached );
			} else {
				elementMatchers.push( cached );
			}
		}

		// Cache the compiled function
        console.log('compile matcherFromGroupMatchers');
		cached = compilerCache( selector, matcherFromGroupMatchers( elementMatchers, setMatchers ) );
        console.log('compile after matcherFromGroupMatchers');
        console.log([cached]);

	}
	return cached;
};

可以看出，compile实际上就是将不同的tokens用matcherFromTokens编译成一个个matcher（两种不同的matcher,setMatcher和elementMatcher）,最后再调用matcherFromGroupMatchers，生成一个superMatcher。

我们接下来看看matcherFromTokens和matcherFromGroupMatchers的源码（注意它是在什么时候把expando加上的，可能还要回到前几篇去看）

function matcherFromTokens( tokens ) {
    console.log('matcherFromTokens begin');
    console.log('arguments:tokens');
    console.log(arguments);
    console.log('matcherFromTokens addCombinator');
	var checkContext, matcher, j,
		len = tokens.length,
		leadingRelative = Expr.relative[ tokens[0].type ],
		implicitRelative = leadingRelative || Expr.relative[" "],
		i = leadingRelative ? 1 : 0,

		// The foundational matcher ensures that elements are reachable from top-level context(s)
		matchContext = addCombinator( function( elem ) {
			return elem === checkContext;
		}, implicitRelative, true ),
		matchAnyContext = addCombinator( function( elem ) {
			return indexOf.call( checkContext, elem ) > -1;
		}, implicitRelative, true ),
		matchers = [ function( elem, context, xml ) {
            console.log('matchers 1 begin');
            console.log('arguments:elem, context, xml');
            console.log(arguments);
			return ( !leadingRelative && ( xml || context !== outermostContext ) ) || (
				(checkContext = context).nodeType ?
					matchContext( elem, context, xml ) :
					matchAnyContext( elem, context, xml ) );
		} ];

	for ( ; i < len; i++ ) {
		if ( (matcher = Expr.relative[ tokens[i].type ]) ) {
            console.log('matcherFromTokens addCombinator '+i);
            console.log('matcherFromTokens addCombinator elementMatcher '+i);
			matchers = [ addCombinator(elementMatcher( matchers ), matcher) ];
            console.log('matcherFromTokens after addCombinator '+i);
            console.log(matchers);
		} else {
            //如果不是连接符
            console.log('matcherFromTokens filter '+i);
			matcher = Expr.filter[ tokens[i].type ].apply( null, tokens[i].matches );
            console.log('matcherFromTokens after filter '+i);
            console.log(matchers);
			// Return special upon seeing a positional matcher
            //expando说明什么？
            //在上面tokens[i].type为child或者pseudo时，matcher有[expando]
            //所以有expando的时候就要加强处理
			if ( matcher[ expando ] ) {
				// Find the next relative operator (if any) for proper handling
				j = ++i;
				for ( ; j < len; j++ ) {
					if ( Expr.relative[ tokens[j].type ] ) {
						break;
					}
				}
                //prefilter,selector,matcher,postFilter,postFinder,postSelector;
                //先看这里传入的参数，对于理解setMatcher非常有帮助，它说明matcherFromTokens用了递归的思想，把tokens切割成两部分，已匹配过的和待查找的
                console.log('matcherFromTokens setMatcher');
				return setMatcher(
					i > 1 && elementMatcher( matchers ),
					i > 1 && toSelector(
						// If the preceding token was a descendant combinator, insert an implicit any-element `*`
						tokens.slice( 0, i - 1 ).concat({ value: tokens[ i - 2 ].type === " " ? "*" : "" })
					).replace( rtrim, "$1" ),
					matcher,
					i < j && matcherFromTokens( tokens.slice( i, j ) ),
					j < len && matcherFromTokens( (tokens = tokens.slice( j )) ),
					j < len && toSelector( tokens )
				);
			}
			matchers.push( matcher );
		}
	}
    console.log('matcherFromTokens elementMatcher');
	return elementMatcher( matchers );
}

在matcherFromTokens里用到了三个函数，addCombinator,setMatcher和elementMatcher，后两者的区别在前面的注释中已经有提及了，当不涉及递归等操作时，使用的就是普通的elementMatcher和addCombinator，elementMatcher的代码非常简单，如下

function elementMatcher( matchers ) {
	return matchers.length > 1 ?
		function( elem, context, xml ) {
			var i = matchers.length;
			while ( i-- ) {
				if ( !matchers[i]( elem, context, xml ) ) {
					return false;
				}
			}
			return true;
		} :
		matchers[0];
}

再看一个短函数addCombinator,增加一个Combinator类型的matcher

function addCombinator( matcher, combinator, base ) {
	var dir = combinator.dir,
		checkNonElements = base && dir === "parentNode",
		doneName = done++;
    //有first代表只检查第一个元素
	return combinator.first ?
		// Check against closest ancestor/preceding element
		function( elem, context, xml ) {
			while ( (elem = elem[ dir ]) ) {
				if ( elem.nodeType === 1 || checkNonElements ) {
					return matcher( elem, context, xml );
				}
			}
		} :

		// Check against all ancestor/preceding elements
		function( elem, context, xml ) {
			var oldCache, outerCache,
            //保证当次dirruns,doneName不变
				newCache = [ dirruns, doneName ];

			// We can't set arbitrary data on XML nodes, so they don't benefit from dir caching
			if ( xml ) {
				while ( (elem = elem[ dir ]) ) {
					if ( elem.nodeType === 1 || checkNonElements ) {
						if ( matcher( elem, context, xml ) ) {
							return true;
						}
					}
				}
			} else {
				while ( (elem = elem[ dir ]) ) {
					if ( elem.nodeType === 1 || checkNonElements ) {
						outerCache = elem[ expando ] || (elem[ expando ] = {});
                        //这里的outerCache也就是一个对象啊？怎么会有dir属性呢，是后面存进去的
						if ( (oldCache = outerCache[ dir ]) &&
							oldCache[ 0 ] === dirruns && oldCache[ 1 ] === doneName ) {

							// Assign to newCache so results back-propagate to previous elements
							return (newCache[ 2 ] = oldCache[ 2 ]);
						} else {
							// Reuse newcache so results back-propagate to previous elements
                            //缓存最让我担心的还是失效时机
							outerCache[ dir ] = newCache;

							// A match means we're done; a fail means we have to keep checking
                            //这里我感觉这个函数的结构设计和matcher是紧耦合的。
							if ( (newCache[ 2 ] = matcher( elem, context, xml )) ) {
								return true;
							}
						}
					}
				}
			}
		};
}

再来看最长的matcher。。。一定要结合上面调用setMatcher时传入的参数一起看

//这TM又是一个奇葩的函数。
//返回一个添加了expando的函数
//让我难以理解的是filter和matcher这两种类型的函数有什么区别,没区别，filter生成matcher
//第1个参数，preFilter，前置过滤器，相当于“div”过滤器
//第2个参数，selector，前置过滤器的字符串格式，相当于“div”input:checked + p
//第3个参数，matcher，当前位置伪类“:first”的匹配器/过滤器
//第4个参数，postFilter，后置过滤器，相当于“ ”
//第5个参数，postFinder，后置搜索器，相当于在前边过滤出来的集合里边再搜索剩下的规则的一个搜索器
//第6个参数，postSelector，后置搜索器对应的选择器字符串，相当于“input:checked + p”
//伪类选择器时会执行这个函数
function setMatcher( preFilter, selector, matcher, postFilter, postFinder, postSelector ) {
	if ( postFilter && !postFilter[ expando ] ) {
		postFilter = setMatcher( postFilter );
	}
	if ( postFinder && !postFinder[ expando ] ) {
		postFinder = setMatcher( postFinder, postSelector );
	}
    //遇到这种闭包函数，要注意对上面参数的使用
    //这里的seed和results有什么区别？
    //results用来存已经可以确定返回的元素
	return markFunction(function( seed, results, context, xml ) {
		var temp, i, elem,
			preMap = [],
			postMap = [],
			preexisting = results.length,

			// Get initial elements from seed or context
            //这里如果没有seed，则获得所有context下的符合selector或*的元素
			elems = seed || multipleContexts( selector || "*", context.nodeType ? [ context ] : context, [] ),

			// Prefilter to get matcher input, preserving a map for seed-results synchronization
            //这行代码执行完后，matcherIn里剩下的元素是elems里通过preFilter过滤的，preMap存的是过滤通过的元素在原elems里的序号，从小到大
			matcherIn = preFilter && ( seed || !selector ) ?
				condense( elems, preMap, preFilter, context, xml ) :
				elems,

			matcherOut = matcher ?
				// If we have a postFinder, or filtered seed, or non-seed postFilter or preexisting results,
                //??????
				postFinder || ( seed ? preFilter : preexisting || postFilter ) ?

					// ...intermediate processing is necessary
					[] :

					// ...otherwise use results directly
					results :
                //如果没有matcher，matcherOut就是matcherIn
				matcherIn;

		// Find primary matches
		if ( matcher ) {
            //????matcher为什么会传入4个参数？看之前的声明只有3个
			matcher( matcherIn, matcherOut, context, xml );
		}

		// Apply postFilter
        //应用尾过滤
		if ( postFilter ) {
            //这里temp基本就是不做任何处理拷贝过来啊
			temp = condense( matcherOut, postMap );
			postFilter( temp, [], context, xml );

			// Un-match failing elements by moving them back to matcherIn

			i = temp.length;
			while ( i-- ) {
				if ( (elem = temp[i]) ) {
                    //这个temp果然是中介，把这些没用到的元素再覆盖到原matcherIn,按照postMap从大到小的顺序，再把matcherOut中的这部分设为false
					matcherOut[ postMap[i] ] = !(matcherIn[ postMap[i] ] = elem);
				}
			}
		}
        //如果还剩seed
		if ( seed ) {
			if ( postFinder || preFilter ) {
                //如果有postFinder?
				if ( postFinder ) {
					// Get the final matcherOut by condensing this intermediate into postFinder contexts
					temp = [];
					i = matcherOut.length;
					while ( i-- ) {
						if ( (elem = matcherOut[i]) ) {
							// Restore matcherIn since elem is not yet a final match
							temp.push( (matcherIn[i] = elem) );
						}
					}
                    //这是一个递归调用的方式
					postFinder( null, (matcherOut = []), temp, xml );
				}

				// Move matched elements from seed to results to keep them synchronized
                //这里有一个两个数组互斥的用法
				i = matcherOut.length;
				while ( i-- ) {
					if ( (elem = matcherOut[i]) &&
						(temp = postFinder ? indexOf.call( seed, elem ) : preMap[i]) > -1 ) {

						seed[temp] = !(results[temp] = elem);
					}
				}
			}

		// Add elements to results, through postFinder if defined
		} else {
			matcherOut = condense(
				matcherOut === results ?
					matcherOut.splice( preexisting, matcherOut.length ) :
					matcherOut
			);
			if ( postFinder ) {
				postFinder( null, results, matcherOut, xml );
			} else {
				push.apply( results, matcherOut );
			}
		}
	});
}

matcherFromTokens通过调用上面三个函数，然后生成了一个个matchers数组，然后compile再调用matcherFromGroupMatchers把这些matchers合并成一个超级matcher

function matcherFromGroupMatchers( elementMatchers, setMatchers ) {
    console.log('matcherFromGroupMatchers begin');
    console.log('arguments：elementMatchers, setMatchers');
    console.log(arguments);
	var bySet = setMatchers.length > 0,
		byElement = elementMatchers.length > 0,
		superMatcher = function( seed, context, xml, results, outermost ) {
            console.log('superMatcher begin');
            console.log('arguments:seed, context, xml, results, outermost');
            console.log(arguments);
			var elem, j, matcher,
				matchedCount = 0,
				i = "0",
				unmatched = seed && [],
				setMatched = [],
				contextBackup = outermostContext,
				// We must always have either seed elements or outermost context
				elems = seed || byElement && Expr.find["TAG"]( "*", outermost ),
				// Use integer dirruns iff this is the outermost matcher
				dirrunsUnique = (dirruns += contextBackup == null ? 1 : Math.random() || 0.1),
				len = elems.length;

			if ( outermost ) {
				outermostContext = context !== document && context;
			}

			// Add elements passing elementMatchers directly to results
			// Keep `i` a string if there are no elements so `matchedCount` will be "00" below
			// Support: IE<9, Safari
			// Tolerate NodeList properties (IE: "length"; Safari: ) matching elements by id
			for ( ; i !== len && (elem = elems[i]) != null; i++ ) {
				if ( byElement && elem ) {
					j = 0;
					while ( (matcher = elementMatchers[j++]) ) {
						if ( matcher( elem, context, xml ) ) {
							results.push( elem );
							break;
						}
					}
					if ( outermost ) {
						dirruns = dirrunsUnique;
					}
				}

				// Track unmatched elements for set filters
                //???????这里有什么用？
				if ( bySet ) {
					// They will have gone through all possible matchers
					if ( (elem = !matcher && elem) ) {
						matchedCount--;
					}

					// Lengthen the array for every element, matched or not
					if ( seed ) {
						unmatched.push( elem );
					}
				}
			}

			// Apply set filters to unmatched elements
			matchedCount += i;
			if ( bySet && i !== matchedCount ) {
				j = 0;
				while ( (matcher = setMatchers[j++]) ) {
                    console.log('matcherFromGroupMatchers matcher '+j);
					matcher( unmatched, setMatched, context, xml );
                    console.log('matcherFromGroupMatchers after matcher '+j);
                    console.log('setMatched');
                    console.log(setMatched);
                    console.log('unmatched');
                    console.log(unmatched);
				}

				if ( seed ) {
					// Reintegrate element matches to eliminate the need for sorting
					if ( matchedCount > 0 ) {
						while ( i-- ) {
							if ( !(unmatched[i] || setMatched[i]) ) {
								setMatched[i] = pop.call( results );
							}
						}
					}

					// Discard index placeholder values to get only actual matches
                    //这里有毛用啊？
					setMatched = condense( setMatched );
				}

				// Add matches to results
                //注意这里用的是apply
                //我TM终于理解为什么会有call和apply这两种语法了。。
				push.apply( results, setMatched );

				// Seedless set matches succeeding multiple successful matchers stipulate sorting
                //没有待选元素了，就可以去除结果里重复的元素了
				if ( outermost && !seed && setMatched.length > 0 &&
					( matchedCount + setMatchers.length ) > 1 ) {
                    console.log('matcherFromGroupMatchers uniqueSort');
					Sizzle.uniqueSort( results );
                    console.log('matcherFromGroupMatchers after uniqueSort');
                    console.log(results);
				}
			}

			// Override manipulation of globals by nested matchers
			if ( outermost ) {
				dirruns = dirrunsUnique;
				outermostContext = contextBackup;
			}

			return unmatched;
		};

	return bySet ?
		markFunction( superMatcher ) :
		superMatcher;
}

嗯，拿到这个superMatcher，剩下的就是调用了，最后我们看看传进去的参数（在select中调用）

	compile( selector, match )(
		seed,
		context,
		!documentIsHTML,
		results,
		rsibling.test( selector ) && testContext( context.parentNode ) || context
	);

Sizzle源码基本就是这样了，接下来的文章我们会继续分析jQuery其他模块。