// a good example
var handlePopup = {

    // 事件句柄，处理所有和event对象有关的东西
    handleClick: function (e) {
 
        // 假设事件支持DOM Level2
        e.preventDefault();
        e.stopPropagation();

        // 传入应用逻辑
        this.showPopup(e.clientX, e.clientY);
    },

    // 应用逻辑，独立于事件、
    showPopup: function(x, y) {
        var popup = document.getElementById("popup");
        popup.style.left = x + "px";
        popup.style.top = y + "px";
    }
};

addListener(element, "click", function(e) {
    handlePopup.handleClick(e);
});