判断节点包含

• 元素包含

contains基本兼容
用法node.contains( otherNode )
compareDocumentPosition感觉比较奇怪,据说是这样

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.（之前看过实现方式的,忘了2333...）当然不是用的contains，因为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 );
}