Js detects whether the network is specifically connected to the function of the code

 
var EventUtil = { 
addHandler: function (element, type, handler) { 
if (element.addEventListener) { 
element.addEventListener(type, handler, false); 
} else if (element.attachEvent) { 
element.attachEvent("on" + type, handler); 
} else { 
element["on" + type] = handler; 
} 
}, 
removeHandler: function (element, type, handler) { 
if (element.removeEventListener) { 
element.removeEventListener(type, handler, false); 
} else if (element.detachEvent) { 
element.detachEvent("on" + type, handler); 
} else { 
element["on" + type] = null; 
} 
} 
}; 

var dom = document.createElement('img'); 
dom.style = 'display:none;'; 
dom.src = 'http://www.baidu.com/img/bdlogo.gif'; 
dom.id = 'map_img'; 
EventUtil.addHandler(dom, 'error', function(){ 

alert(' Your computer does not have a link to the network, connect to the network to open the map! '); 
}); 
document.body.appendChild(dom);