对于某些元素执行click()不生效，采用模拟鼠标click事件

/**模拟click事件*/
function simulate_click(elem) {
    if (document.createEvent) {
        var e = document.createEvent("MouseEvents");
        e.initMouseEvent("click", true, true, window, 0, 0, 0, 0, 0, false, false, false, false, 0, null);
        elem[0].dispatchEvent(e);
   } else if (element.fireEvent) {
        elem[0].fireEvent("onclick");
  }
}