简单其实不简单

contains()函数使用一例

今天看到的，让我了解了下compareDocumentPosition()、contains()函数，以后判断是否在元素上面就有新方法了。其它的也没什么好说，看下Demo吧！

window.onload = function () {
    document.getElementById('dropdown').onmouseover = openMenu;
}

function openMenu(e) {
    var evt = e || window.event;
    var tgt = evt.target || evt.srcElement;
    while (tgt.nodeName !== 'LI') {
        if (tgt.nodeName === 'HTML') {
            return;
        }
        tgt = tgt.parentNode;
    }
    var nested = tgt.getElementsByTagName('ul')[0];
    if (nested) {
        nested.className = 'open';
        tgt.onmouseout = function (e) {
            var evt = e || window.event;
            var related = evt.relatedTarget || evt.toElement;
            if (!nested.contains(related)) {
                nested.className = '';
                tgt.onmouseout = null;
            }
        }
    }
}

/* Bloody Firefox STILL doesn't support contains */

if (window.Node && Node.prototype && !Node.prototype.contains) {
    Node.prototype.contains = function (arg) {
        return !!(this.compareDocumentPosition(arg) & 16)
    }
}