node.js中的through2和native Transform stream有什么区别？

Question

In the through2 docs , it says:

A tiny wrapper around Node.js streams.Transform (Streams2/3) to avoid explicit subclassing noise.

What is meant by that? What is this " subclassing noise "?

Answer 1

Common implementation on transform stream looks like:

ES5 syntax

const { Transform } = require('stream');
const util = require('util');

function MyTransform(options) {
  if (!(this instanceof MyTransform))
    return new MyTransform(options);
  Transform.call(this, options);
}
util.inherits(MyTransform, Transform);

MyTransform.prototype._transform = function (chunk, enc, cb) {
  // do some data transformation
  this.push(chunk);
  cb();
};

ES6 syntax

const { Transform } = require('stream');

class MyTransform extends Transform {
  constructor(options) {
    super(options);
  }

  _transform(chunk, encoding, cb) {
    // do some data transformation
    this.push(chunk)
    cb()
  }
}

As you can see, to implement transform stream you have to write some boilerplate code, like extending Transform interface etc.

By using through2 you just write your transformation function. Profit.

Answer 2

In the through2 docs it also says (nowadays):

Since Node.js introduced Simplified Stream Construction, many uses of through2 have become redundant.

The example by Rezvan above would then become:

const { Transform } = require('stream');

return new Transform({
  transform(chunk, encoding, cb) {
    // do some data transformation
    this.push(chunk);
    cb();
  }
});