node.js - 带有字符串的可读ObjectMode

我试图了解流如何在nodejs中工作。为此，我编写了这段代码

'use strict'

var fs = require('fs')
var split = require('split')
var stream = require('stream')

const myTransform = new stream.Transform({
  writableObjectMode: true,
  readableObjectMode: true,
  transform (chunk, encoding, callback) {
    console.log('transform', chunk) // chunk is a string
    this.push({chunk: chunk})
    callback()
  }
})

const myWritable = new stream.Writable({
  objectMode: true,
  write (chunk, encoding, callback) {
    console.log('writable', chunk)
    callback()
  }
})

myWritable.on('finish', () => console.log('FINISHED'))
fs.createReadStream(__dirname + '/prova.txt')
  .pipe(split())
  .pipe(myTransform)
  .pipe(myWritable)

此示例运行良好，但我不明白为什么如果转换流将readableObjectMode设置为false，脚本将失败

transform line1
stream.js:74
      throw er; // Unhandled stream error in pipe.
      ^

TypeError: Invalid non-string/buffer chunk
    at chunkInvalid (_stream_readable.js:380:10)
    at readableAddChunk (_stream_readable.js:125:12)
    at Transform.Readable.push (_stream_readable.js:111:10)
    at Transform.push (_stream_transform.js:128:32)
    at Transform.transform [as _transform]    (/path/to/mystream.js:12:10)
    at Transform._read (_stream_transform.js:167:10)
    at Transform._write (_stream_transform.js:155:12)
    at doWrite (_stream_writable.js:301:12)
    at writeOrBuffer (_stream_writable.js:287:5)
    at Transform.Writable.write (_stream_writable.js:215:11)

最佳答案

该文档不是很清楚，但是


readableObjectMode相对于“读取侧”。因此，如果为true，则可以推动对象。否则，必须使用字符串或缓冲区
writableObjectMode相对于“写面”。因此，方法transform具有一个对象作为第一个参数。


因此，在上面的示例中，writableObjectMode参数可以设置为false。

注意：如果writableObjectMode设置为false，则transform方法将Buffer的实例接收为chunk