代码很简单直接上源码
function winnow( elements, qualifier, not ) {
//如果qualifier是函数
if ( jQuery.isFunction( qualifier ) ) {
//not为true时,返回qualifier返回false的elements
//not为false时,返回qualifier返回true的elements
return jQuery.grep( elements, function( elem, i ) {
/* jshint -W018 */
return !!qualifier.call( elem, i, elem ) !== not;
});
}
//如果qualifier是DOM元素
if ( qualifier.nodeType ) {
//not为true时,返回elements中和qualifier不是同一元素的elements
//not为false时,返回elements中和qualifier是同一元素的elements
return jQuery.grep( elements, function( elem ) {
return ( elem === qualifier ) !== not;
});
}
//如果qualifier是字符串(将qualifier当成selector)
if ( typeof qualifier === "string" ) {
// 如果selector不是多级selector(多级selector:div #id)或多selector(selector, selector)
// 直接调用jQuery.filter( qualifier, elements, not )返回结果
// risSimple = /^.[^:#\[\.,]*$/
if ( risSimple.test( qualifier ) ) {
return jQuery.filter( qualifier, elements, not );
}
// 如果selector是多级selector(多级selector:div #id)或多selector(selector, selector)
// 解释: 因为多级selector或selector无法直接加上:not组成伪类选择器
// 所以先过滤,再遍历根据not参数过滤
qualifier = jQuery.filter( qualifier, elements );
}
return jQuery.grep( elements, function( elem ) {
return ( indexOf.call( qualifier, elem ) >= 0 ) !== not;
});
}
/**
* filter方法是对自身进行筛选
* find方法是对子集进行查找或匹配
*/
jQuery.filter = function( expr, elems, not ) {
var elem = elems[ 0 ];
//如果有not参数,修正selector为not伪类表达式
if ( not ) {
expr = ":not(" + expr + ")";
}
return elems.length === 1 && elem.nodeType === 1 ?
//只有一个元素看是否和表达式匹配
jQuery.find.matchesSelector( elem, expr ) ? [ elem ] : [] :
jQuery.find.matches( expr, jQuery.grep( elems, function( elem ) {
return elem.nodeType === 1;
}));
};
jQuery.fn.extend({
find: function( selector ) {
var i,
len = this.length,
ret = [],
self = this;
// example:
// var e = document.getElementById('a');
// var $li = $('div').find(e);
if ( typeof selector !== "string" ) {
return this.pushStack( jQuery( selector ).filter(function() {
for ( i = 0; i < len; i++ ) {
// this指向jQuery( selector )迭代的当前元素
// 如果调用.find(selector)的JQuery对象中的的某个元素包含selector,返回true
if ( jQuery.contains( self[ i ], this ) ) {
return true;
}
}
}) );
}
//$('ul').find('li');
for ( i = 0; i < len; i++ ) {
jQuery.find( selector, self[ i ], ret );
}
// Needed because $( selector, context ) becomes $( context ).find( selector )
// 删除重复元素
ret = this.pushStack( len > 1 ? jQuery.unique( ret ) : ret );
// 拼接调用者和selector,example,$(div).find('ul'),ret.selector为div ul
ret.selector = this.selector ? this.selector + " " + selector : selector;
return ret;
},
// 保留匹配selector的元素
filter: function( selector ) {
return this.pushStack( winnow(this, selector || [], false) );
},
// 删除匹配selector的元素
not: function( selector ) {
return this.pushStack( winnow(this, selector || [], true) );
},
// 如果调用的jquery元素有一个符合selector返回true
is: function( selector ) {
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;
}