socket.connecting
如果为 true，socket.connect(options[, connectListener]) 已被调用但尚未完成。在套接字连接之前，它将保持为 true，然后在套接字连接后被设置为 false 并触发 'connect' 事件。请注意，socket.connect(options[, connectListener]) 的回调函数是 'connect' 事件的监听器。
【If true,
socket.connect(options[, connectListener]) was
called and has not yet finished. It will stay true until the socket becomes
connected, then it is set to false and the 'connect' event is emitted. Note
that the
socket.connect(options[, connectListener])
callback is a listener for the 'connect' event.】