上篇說道,tokenize方法會把selector分割成一個個selector邏輯單元(如div>a是三個邏輯單元 'div','>','a')併爲之片段賦予對應類型的過濾函數。
for ( type in Expr.filter ) {
if ( (match = matchExpr[ type ].exec( soFar )) && (!preFilters[ type ] ||
(match = preFilters[ type ]( match ))) ) {
matched = match.shift();
tokens.push({
value: matched,
type: type,
matches: match
});
soFar = soFar.slice( matched.length );
}
}
然後選出最後selector邏輯單元(是指由需要上下文的選擇器,如id,tag,class等)所對應的元素集作爲從右向左(一般情況)過濾的候選元素集,match(正則捕獲組)是selector邏輯片段的解析結果(如[arr="111"]根據正則解析爲arr,",=,111 ),在selector邏輯片段是ATTR、CHILD、PSEUDO是需要調用preFilter對match進行修正.
preFilter: {
//match是捕獲組
//假設:[arr^='val']
"ATTR": function( match ) {
//attr的第一個捕獲 組是arr,將其中的轉碼變成原來的字符
match[1] = match[1].replace( runescape, funescape );
// Move the given value to match[3] whether quoted or unquoted
// 將val放到捕獲組3裏,原來的捕獲組3捕獲'或"
match[3] = ( match[4] || match[5] || "" ).replace( runescape, funescape );
//如果捕獲組2是~=,在match[3]前後加空格,以方便匹配單個單詞
if ( match[2] === "~=" ) {
match[3] = " " + match[3] + " ";
}
//match[0] = '[arr^='val']'
//match[1] = 'arr'
//match[2] = '='
//match[3] = '111'
return match.slice( 0, 4 );
},
"CHILD": function( match ) {
/* 例如nth-child(-2n+1)的捕獲組
mathc[1] nth
mathc[2] child
mathc[3] 2n+1
mathc[4] 2n
mathc[5] -
mathc[6] 2
mathc[7] +
mathc[8] 1
*/
match[1] = match[1].toLowerCase();
// nth必須需要參數
if ( match[1].slice( 0, 3 ) === "nth" ) {
// nth-* requires argument
if ( !match[3] ) {
Sizzle.error( match[0] );
}
// numeric x and y parameters for Expr.filter.CHILD
// remember that false/true cast respectively to 0/1
// xn + y
// 將even,odd修正爲xn+y,match[4]修正爲+-x
match[4] = +( match[4] ? match[5] + (match[6] || 1) : 2 * ( match[3] === "even" || match[3] === "odd" ) );
// 將match[5]替換爲+-y
match[5] = +( ( match[7] + match[8] ) || match[3] === "odd" );
// other types prohibit arguments
// 除nth外其他類型禁止參數
} else if ( match[3] ) {
Sizzle.error( match[0] );
}
// match[0] :nth-child(-2n+1)
// match[1] nth
// match[2] child
// match[3] -2n+1
// match[4] -2
// match[5] 1
// match[6] 2
// match[7] +
// match[8] 1
return match;
},
/**
* match[1] :後僞類類型
* match[2] 僞類參數
* match[3] 參數中的'或者"
* match[4] 除去'或"的僞類
*/
"PSEUDO": function( match ) {
var excess,
unquoted = !match[5] && match[2];
//是CHILD僞類,返回null
if ( matchExpr[ "CHILD"].test( match[0] ) ) {
return null;
}
// Accept quoted arguments as-is
// 參數有引號
//將match[2]替換爲無引號的match[4]參數
if ( match[3] && match[4] !== undefined ) {
match[2] = match[4];
// Strip excess characters from unquoted arguments
// 除去帶引號的參數的多餘字符
} else if ( unquoted && rpseudo.test( unquoted ) &&
// Get excess from tokenize (recursively)
//excess多餘字符的長度
(excess = tokenize( unquoted, true )) &&
//excess多餘參數的索引位置,excess是個負值,以便截取到多餘字符之前
(excess = unquoted.indexOf( ")", unquoted.length - excess ) - unquoted.length) ) {
// excess is a negative index
match[0] = match[0].slice( 0, excess );
match[2] = unquoted.slice( 0, excess );
}
// Return only captures needed by the pseudo filter method (type and argument)
return match.slice( 0, 3 );
}
}