Node.js Design Patterns/

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Readable Streams: Simplified Construction and Iterables

Readable Streams: Simplified Construction and Iterables

Learn how to implement simple custom streams using the simplified construction approach.

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Simplified construction

For simple custom streams, we can avoid creating a custom class by using the Readable stream’s simplified construction approach. With this approach, we only need to invoke new Readable(options) and pass a method named read() in the set of options. The read() method here has exactly the same semantic as the _read() method that we saw in the class extension approach. Let's rewrite our RandomStream using the simplified constructor approach.

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Node.js
import { Readable } from 'stream'
import Chance from 'chance'
const chance = new Chance()
let emittedBytes = 0
const randomStream = new Readable({
  read (size) {
    const chunk = chance.string({ length: size })
    this.push(chunk, 'utf8')
    emittedBytes += chunk.length
    if (chance.bool({ likelihood: 5 })) {
      this.push(null)
    }
  }
})
randomStream
  .on('data', (chunk) => {
    console.log(`Chunk received (${chunk.length} bytes): ${chunk.toString()}`)
  })
  .on('end', () => {
    console.log(`Produced ${emittedBytes} bytes of random data`)
  })

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