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This is a super thin wrapper around through2 that works like Array.prototype.filter but for streams.

For when through2 is just too verbose ūüėČ

Note you will NOT be able to alter the content of the chunks. This is intended for filtering only. If you want to modify the stream content, use either through2 or through2-map.

var filter = require("through2-filter")
var skip = filter(function (chunk) {
  // skip buffers longer than 100 
  return chunk.length < 100
// vs. with through2: 
var skip = through2(function (chunk, encoding, callback) {
  // skip buffers longer than 100 
  if (chunk.length < 100) this.push(chunk)
  return callback()
// Then use your filter: 
// Additionally accepts `wantStrings` argument to conver buffers into strings 
var alphanum = new RegExp("^[A-Za-z0-1]+$")
var scrub = filter({wantStrings: true}, function (str) {
  return alphanum.exec(str)
// Works like `Array.prototype.filter` meaning you can specify a function that 
// takes up to two* arguments: fn(element, index) 
var skip10 = filter(function (element, index) {
  return index > 10

*Differences from Array.prototype.filter:

  • No third array callback argument. That would require realizing the entire stream, which is generally counter-productive to stream operations.
  • Array.prototype.filter doesn't modify the source Array, which is somewhat nonsensical when applied to streams.


require("through2-filter")([options], fn)

Create a through2-filter instance that will call fn(chunk). If fn(chunk) returns "true" the chunk will be passed downstream. Otherwise it will be dropped.

require("through2-filter").ctor([options], fn)

Create a through2-filter Type that can be instantiated via new Type() or Type() to create reusable spies.

require("through2-filter").obj([options], fn)

Create a through2-filter that defaults to objectMode = true.

require("through2-filter").objCtor([options], fn)

Create a through2-filter Type that defaults to objectMode = true.


  • wantStrings: Automatically call chunk.toString() for the super lazy.
  • all other through2 options