参考Soket.IO官方文档：https://socket.io/docs/client-api/，客户端内置事件一共有10种，测试代码如下：

socket.on('connect', function(data){

    onlineFlag = true;     console.log(data + ' - connect'); }); socket.on('connect_error', function(data){     console.log(data + ' - connect_error'); }); socket.on('connect_timeout', function(data){     console.log(data + ' - connect_timeout'); }); socket.on('error', function(data){     console.log(data + ' - error'); }); socket.on('disconnect', function(data){     onlineFlag = false;     console.log(data + ' - disconnect'); }); socket.on('reconnect', function(data){     console.log(data + ' - reconnect'); }); socket.on('reconnect_attempt', function(data){     console.log(data + ' - reconnect_attempt'); }); socket.on('reconnecting', function(data){     console.log(data + ' - reconnecting'); }); socket.on('reconnect_error', function(data){     console.log(data + ' - reconnect_error'); }); socket.on('reconnect_failed', function(data){     console.log(data + ' - reconnect_failed'); }); socket.on('ping', function(data){     console.log(data + ' - ping'); }); socket.on('pong', function(data){     console.log(data + ' - pong'); });

流程图