当有了离线支持，失去连接信号并不意味着数据会被丢失。

But with offline support, a dropped signal doesn't mean lost data.

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当失去连接或从服务器端断开时在客户端调用。

Called on the client when the connection was lost or you disconnected from the server.

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使用异步交换能够避免失去连接(因为服务器维护等等)以及因此而失去响应的风险。

Using an asynchronous exchange avoids the risk of losing the connection (because of server maintenance and so on) and, thus, the response.

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