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。