'data' 事件

• chunk <Buffer> | <string> | <any> 数据块。 对于不在对象模式下操作的流，块将是字符串或 Buffer。 对于处于对象模式的流，块可以是除 null 之外的任何 JavaScript 值。

每当流将数据块的所有权移交给消费者时，则会触发 'data' 事件。 每当通过调用 readable.pipe()、readable.resume()、或通过将监听器回调绑定到 'data' 事件而将流切换到流动模式时，就会发生这种情况。 每当调用 readable.read() 方法并且可以返回数据块时，也会触发 'data' 事件。

将 'data' 事件监听器绑定到尚未显式暂停的流，则会将流切换到流动模式。 数据将在可用时立即传入。

如果使用 readable.setEncoding() 方法为流指定了默认编码，则监听器回调将把数据块作为字符串传入；否则数据将作为 Buffer 传入。

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

• chunk <Buffer> | <string> | <any> The chunk of data. For streams that are not operating in object mode, the chunk will be either a string or Buffer. For streams that are in object mode, the chunk can be any JavaScript value other than null.

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.

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.

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.`);
});