Sizzle选择器引擎介绍

(function(window, undefined) {
    var jQuery = function (selector, context) {
        return new  jQuery.fn.init(selector, context, rootjQuery);
    }
    jQuery.fn = jQuery.prototype = {...}
    jQuery.fn.init.prototype = jQuery.fn;
    // utilities method
    // Deferred
    // support
    // Data cache
    // queue
    // Attribute
    // Event
    // Sizzle about 2k lines
    // DOM
    // css operation
    // Ajax
    // animation
    // position account
    window.jQuery  = window.$ = jQuery;
})

do {
        chunker.exec( "" ); // chunker.lastIndex = 0
        m = chunker.exec( soFar );
        if ( m ) {
            soFar = m[3];
            parts.push( m[1] );
            if ( m[2] ) {
                extra = m[3];
                break;
            }
        }
    } while ( m );

for example：
$(‘#J-con  ul>li:gt(2)’) 解析后的结果为：
parts = ["#J-con", "ul", ">", “li:gt(2)"]
extra = undefined

$(‘#J-con  ul>li:gt(2), div.menu’) 解析后的结果为：
parts = ["#J-con", "ul", ">", “li:gt(2)"]
extra = ‘div.menu’

// Expr.order = [“ID”, [ “CLASS”], “NAME”, “TAG ]
for ( i = 0, len = Expr.order.length; i < len; i++ ) {
    ……
    if ( (match = Expr.leftMatch[ type ].exec( expr )) ) {
        set = Expr.find[ type ]( match, context);
        expr = expr.replace( Expr.match[ type ], "" );
    }
}

Sizzle.filter = function( expr, set, inplace, not ) {
    for ( type in Expr.filter ) { //filter： {PSEUDO, CHILD, ID, TAG, CLASS, ATTR, POS}
        //   Expr.leftMatch：确定selector的类型
        if ( (match = Expr.leftMatch[ type ].exec( expr )) != null && match[2] ) {
            // 过滤前预处理，保证格式的规范化
            match = Expr.preFilter[ type ]( match, curLoop, inplace, result, not, isXMLFilter );
            // 进行过滤操作
            found = Expr.filter[ type ]( item, match, i, curLoop );
            // if inplace== true,得到新数组对象；
            if ( inplace && found != null ) {
                if ( pass ) { anyFound = true; } else { curLoop[i] = false; }
            } else if ( pass ) {
                result.push( item );
            }
        }
    }
}

// 从左到后时，位置伪类处理方法
var posProcess = function( selector, context, seed ) {
	var match,
       tmpSet = [],
       later = "",
       root = context.nodeType ? [context] : context;
    // 先剔除位置伪类，保存在later里面
    while ( (match = Expr.match.PSEUDO.exec( selector )) ) {
    	later += match[0];
       selector = selector.replace( Expr.match.PSEUDO, "" );
    }

    selector = Expr.relative[selector] ? selector + "*" : selector;
    // 在不存在位置伪类的情况下，进行查找
    for ( var i = 0, l = root.length; i < l; i++ ) {
    	Sizzle( selector, root[i], tmpSet, seed );
    }
    // 以位置伪类为条件，对结果集合进行过滤
    return Sizzle.filter( later, tmpSet );
};

// 如果selector expression 最左边是#ID，则计算出#ID选择器，缩小执行上下文
if(parts[0] is #id) {
    context = Sizzle.find(parts.shift(), context)[0];
}
if (context) {
    // 得到最后边块表达式的元素集合
    ret = Sizzle.find(parts.pop(), context);
    // 对于刚刚得到的元素集合，进行块内元素过滤
    set = Sizzle.filter(ret.expr, ret.set) ;
    // 不断过滤
    while(parts.length) {
        pop = parts.pop();
        ……
        Expr.relative[ cur ]( checkSet, pop );
    }
}

"+": function(checkSet, part){
    var isPartStr = typeof part === "string",
        isTag = isPartStr && !rNonWord.test( part ),   //判断过滤selector是否为标签选择器
        isPartStrNotTag = isPartStr && !isTag;
    if ( isTag ) {
        part = part.toLowerCase();
    }
    for ( var i = 0, l = checkSet.length, elem; i < l; i++ ) {
        if ( (elem = checkSet[i]) ) {
            while ( (elem = elem.previousSibling) && elem.nodeType !== 1 ) {}
            checkSet[i] = isPartStrNotTag || elem && elem.nodeName.toLowerCase() === part ?
                elem || false :
                elem === part;
        }
    }
    if ( isPartStrNotTag ) {
        Sizzle.filter( part, checkSet, true );
    }
}