Filtering Stream object in node.js

Question

It seems to me that an elegant way to process certain kinds of data in Node.js would be to chain processing objects, like UNIX pipes.

For example, grep:

Answer 1

Although the answer that exists is nice, it still requires a bit of digging around on behalf of those looking for answers.

The following code completes the example the OP gave, using the Node 0.10 stream API.

var stream = require('stream')
var util = require('util')

function Grep(pattern) {
  stream.Transform.call(this)

  this.pattern = pattern
}

util.inherits(Grep, stream.Transform)

Grep.prototype._transform = function(chunk, encoding, callback) {
  var string = chunk.toString()

  if (string.match(this.pattern)) {
    this.push(chunk)
  }

  callback()
}

var grep = new Grep(/foo/)
process.stdin.pipe(grep)
grep.pipe(process.stdout)