判断节点包含

• 元素包含

contains基本兼容
用法node.contains( otherNode )
compareDocumentPosition感受比较奇怪,听说是这样

The Node.compareDocumentPosition() method compares the position of the
current node against another node in any other document.
返回值分为6个数字
jquery的selector-native有个原生方法contains这样写的

contains: function( a, b ) {
    var adown = a.nodeType === 9 ? a.documentElement : a, 
        bup = b && b.parentNode;
    return a === bup || !!( bup && bup.nodeType === 1 &&  adown.contains(bup) );
    }

比较容易理解

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update 2015-01-27

开发凤凰焦点项目的时候，有用到判断元素包含关系的contains,当时第一反应是想到jquery取子元素的方式.（以前看过实现方式的,忘了2333...）固然不是用的contains，由于相比取子元素更适合关系判断.那么jq是怎么取的呢？

• node.nextSibling
• node.previousSibling
  没错，就是这俩属性,traversing.js脚本可见

jQuery.extend({

    //direction
    dir: function( elem, dir, until ) {
        var matched = [],
            truncate = until !== undefined;

        while ( (elem = elem[ dir ]) && elem.nodeType !== 9 ) {
            if ( elem.nodeType === 1 ) {     //nodeType:1 --> element
                if ( truncate && jQuery( elem ).is( until ) ) {
                    break;
                }
                matched.push( elem );
            }
        }
        return matched;
    },
    
    sibling: function( n, elem ) {
        var matched = [];

        for ( ; n; n = n.nextSibling ) {
            if ( n.nodeType === 1 && n !== elem ) {
                matched.push( n );
            }
        }

        return matched;
    }
});

siblings: function( elem ) {
    return jQuery.sibling( ( elem.parentNode || {} ).firstChild, elem );
},
children: function( elem ) {
    return jQuery.sibling( elem.firstChild );
}