之所以把这部分放在这里，是因为这里用到了一些基本API，前一篇介绍过后才能使用。
//jQuery通过find方法调用Sizzle引擎
//jQuery通过find方法调用Sizzle引擎
jQuery.find = Sizzle;
jQuery.expr = Sizzle.selectors;
jQuery.expr[":"] = jQuery.expr.pseudos;
jQuery.unique = Sizzle.uniqueSort;
jQuery.text = Sizzle.getText;
jQuery.isXMLDoc = Sizzle.isXML;
jQuery.contains = Sizzle.contains;
var rneedsContext = jQuery.expr.match.needsContext;
//匹配没有其他如class等任何属性的标签，就是简单标签，
//如<input />和<div></div>
var rsingleTag = (/^<(\w+)\s*\/?>(?:<\/\1>|)$/);
//当selector为 .header这样的形式则为简单选择符
var risSimple = /^.[^:#\[\.,]*$/;
// Implement the identical functionality for filter and not
//比较难啃的一个函数，传入参数有几种用法。后面的多个过滤函数都依赖于这个函数
//第一个参数表示element元素集，第二个参数传入过滤函数、DOM、选择符、数组，第三个参数为预设结果
function winnow( elements, qualifier, not ) {
if ( jQuery.isFunction( qualifier ) ) {
return jQuery.grep( elements, function( elem, i ) {
/* jshint -W018 */
return !!qualifier.call( elem, i, elem ) !== not;
});
}
if ( qualifier.nodeType ) {
return jQuery.grep( elements, function( elem ) {
return ( elem === qualifier ) !== not;
});
}
if ( typeof qualifier === "string" ) {
if ( risSimple.test( qualifier ) ) {
return jQuery.filter( qualifier, elements, not );
}
qualifier = jQuery.filter( qualifier, elements );
}
return jQuery.grep( elements, function( elem ) {
return ( jQuery.inArray( elem, qualifier ) >= 0 ) !== not;
});
}
//过滤函数
jQuery.filter = function( expr, elems, not ) {
var elem = elems[ 0 ];
if ( not ) {
expr = ":not(" + expr + ")";
}
//其实这两个区别不大，都要调用Sizzle
return elems.length === 1 && elem.nodeType === 1 ?
jQuery.find.matchesSelector( elem, expr ) ? [ elem ] : [] :
jQuery.find.matches( expr, jQuery.grep( elems, function( elem ) {
return elem.nodeType === 1;
}));
};
//开始jQuery对象的原型进行扩展
jQuery.fn.extend({
find: function( selector ) {
var i,
ret = [],
self = this,
len = self.length;
//当传入的参数是字符串类型时，调用下面的filter方法，本质是调用上面的winnow，winnow里又视情况调用sizzle
if ( typeof selector !== "string" ) {
return this.pushStack( jQuery( selector ).filter(function() {
console.log(‘find‘);
console.log(self);
for ( i = 0; i < len; i++ ) {
//如果self包含符合selector的this，注意这里的this是新的jQuery对象
if ( jQuery.contains( self[ i ], this ) ) {
return true;
}
}
}) );
}
//否则以self[i]为查找上下文context进行查找
for ( i = 0; i < len; i++ ) {
jQuery.find( selector, self[ i ], ret );
}
// Needed because $( selector, context ) becomes $( context ).find( selector )
//这里是正常的压栈和选择符拼接
ret = this.pushStack( len > 1 ? jQuery.unique( ret ) : ret );
ret.selector = this.selector ? this.selector + " " + selector : selector;
return ret;
},
filter: function( selector ) {
return this.pushStack( winnow(this, selector || [], false) );
},
not: function( selector ) {
return this.pushStack( winnow(this, selector || [], true) );
},
is: function( selector ) {
//通过winnow返回的长度来判断
return !!winnow(
this,
// If this is a positional/relative selector, check membership in the returned set
// so $("p:first").is("p:last") won‘t return true for a doc with two "p".
typeof selector === "string" && rneedsContext.test( selector ) ?
jQuery( selector ) :
selector || [],
false
).length;
}
});