JQuery日記_5.14 Sizzle選取器(七)

標籤：style   blog   class   code   c   java   

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‘)並為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(是指由需要內容相關的選取器,如id,tag,class等)所對應的元素集作為從右向左(一般情況)過濾的候選元素集,match(正則擷取的群組)是selector邏輯片段的解析結果(如[arr="111"]根據正則解析為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是擷取的群組             //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元                  match[1] = match[1].replace( runescape, funescape );                   // Move the given value to match[3] whether quoted or unquoted                   // 將val放到擷取的群組3裡，原來的擷取的群組3捕獲‘或"                  match[3] = ( match[4] || match[5] || "" ).replace( runescape, funescape );                   //如果擷取的群組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)的擷取的群組                        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修正為xn+y,match[4]修正為+-x                        match[4] = +( match[4] ? match[5] + (match[6] || 1) : 2 * ( match[3] === "even" || match[3] === "odd" ) );                         // 將match[5]替換為+-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] :後偽類類型             * match[2] 偽類參數             * match[3] 參數中的‘或者"             * match[4] 除去‘或"的偽類             */             "PSEUDO": function( match ) {                   var excess,                        unquoted = !match[5] && match[2];                   //是CHILD偽類，返回null                   if ( matchExpr[ "CHILD"].test( match[0] ) ) {                         return null;                  }                   // Accept quoted arguments as-is                   // 參數有引號                   //將match[2]替換為無引號的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元                  } else if ( unquoted && rpseudo.test( unquoted ) &&                         // Get excess from tokenize (recursively)                         //excess多餘字元的長度                        (excess = tokenize( unquoted, true )) &&                         //excess多餘參數的索引位置,excess是個負值,以便截取到多餘字元之前                        (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 );            }      }