事件：'data'

【Event: 'data'】

• chunk <Buffer> | <string> | <any> 数据块。对于不以对象模式运行的流，数据块将是字符串或 Buffer。对于以对象模式运行的流，数据块可以是任意 JavaScript 值，但不能是 null。

'data' 事件会在流将数据块的所有权交给消费者时触发。每当通过调用 readable.pipe()、readable.resume() 或为 'data' 事件附加监听回调将流切换为流动模式时，都可能发生这种情况。每当调用 readable.read() 方法且有可返回的数据块时，'data' 事件也会被触发。

【The 'data' event is emitted whenever the stream is relinquishing ownership of a chunk of data to a consumer. This may occur whenever the stream is switched in flowing mode by calling readable.pipe(), readable.resume(), or by attaching a listener callback to the 'data' event. The 'data' event will also be emitted whenever the readable.read() method is called and a chunk of data is available to be returned.】

将 'data' 事件监听器附加到未明确暂停的流上，会使流切换到流动模式。数据将会在可获取时立即传递。

【Attaching a 'data' event listener to a stream that has not been explicitly paused will switch the stream into flowing mode. Data will then be passed as soon as it is available.】

如果流使用 readable.setEncoding() 方法指定了默认编码，监听器回调将以字符串形式接收数据块；否则，数据将以 Buffer 形式传递。

【The listener callback will be passed the chunk of data as a string if a default encoding has been specified for the stream using the readable.setEncoding() method; otherwise the data will be passed as a Buffer.】

const readable = getReadableStreamSomehow();
readable.on('data', (chunk) => {
  console.log(`Received ${chunk.length} bytes of data.`);
}); 拷贝