转js contains 方法

function Jcontains(root, el) { 
    if (root.compareDocumentPosition) 
        return root === el || !!(root.compareDocumentPosition(el) & 16); 
        if (root.contains && el.nodeType === 1){ 
            return root.contains(el) && root !== el; 
    } 
    while ((el = el.parentNode)) 
    if (el === root) return true; 
    return false; 
}