document.oncontextmenu = function(ev) {
   //相容IE 谷歌
    var oEvent = ev || event;
    
    var oUl = document.getElementById('ul1');
    //右鍵顯示出來
    oUl.style.display = 'block';
    //跟隨滑鼠
    oUl.style.left = oEvent.clientX + 'px';
    //跟隨滑鼠
    oUl.style.top = oEvent.clientY + 'px';

    return false;
};

document.onclick = function({
    var oUl = document.getElementById('ul1');
    
    oUl.style.display = 'none';
};


<ul id="ul1">
	<li>登陸</li>
	<li>回到首頁</li>
	<li>登出</li>
	<li>加入vip</li>
</ul>

#ul1{
	width: 100px;
	background: #ccc;
	border: 1px solid black;
	position: absolute;
	display: none;
}