Sculpt

A collection of Node.js transform stream utilities for simple data manipulation.

Install with npm install sculpt --save.

API

All of Sculpt's streams operate in objectMode, so be careful that you know what data types are going in and coming out of your streams. Normally Node.js streams are guaranteed to be strings or buffers, but that is not the case when streams operate in object mode.

Methods

Builders

• Map
• Filter

Strings

• Append
• Prepend
• Replace
• Split
• Byte Length

Objects

• Join
• Invoke

Control Flow

• Fork
• Tap

Miscellaneous

• Pipes

Map

Arguments

• callback: A function to apply to each chunk. The functions result is injected into the stream in place of the chunk.

var stream = sculpt.map(function (chunk) {
  return chunk + chunk
})

stream.pipe(process.stdout)
stream.write('hello')

// hellohello

Map can also operate asynchronously. To make the stream async, pass a second argument (a done callback) and call .async().

var stream = sculpt.map(function (chunk, done) {
  requestRemoteData(chunk, function (err, data) {
    done(err, chunk + data)
  })
}).async()

stream.pipe(process.stdout)
stream.write('hello')

// 'hello some remote data...'

Map streams can also operate in multi mode, which lets them push multiple unique values in a single callback. Callbacks in multi mode must return arrays, and each item will be pushed individually. To create a map steam in multi mode call .multi().

This is most useful when you're consuming the output with another stream that depends on meaningful items in each push. This is how the split stream is implemented.

var i = 0
var stream = sculpt.map(function (chunk) {
  i++
  return [i.toString(), chunk]
}).multi()

stream.pipe(process.stdout)
stream.write('hello')

// 1hello

Map streams can be set to ignore values that are undefined. Ordinarily Node.js treats null-ish values (including undefined) as signaling the end of a stream. In some cases it's useful to be able to avoid pushing data for some inputs without having a separate stream to filter the data — for example, cases where deciding whether you want to push data requires expensive computation. In those cases, you can set the stream to ignore undefined values.

var stream = sculpt.map(function (chunk) {
  if (chunk === 'hello') return
  return chunk
}).ignoreUndefined()

stream.pipe(process.stdout)
stream.write('hello')
strea.write('world')

// world

Filter

Arguments

• callback: A truth test to apply to each chunk. If the callback returns false, the chunk is removed from the stream.

var stream = sculpt.filter(function (chunk) {
  return chunk.toString().length >= 5
})

stream.on('data', console.log.bind(console))
stream.write('hi')
stream.write('hello')
stream.write('goodbye')

// 'hellogoodbye'

Filter can also operate asynchronously. To make the stream async, pass a second argument (a done callback) and call .async().

var stream = sculpt.filter(function (chunk, done) {
  requestRemoteValidation(chunk, function (err, valid) {
    done(err, !! valid)
  })
}).async()

stream.on('data', console.log.bind(console))
stream.write('hi')
stream.write('hello')
stream.write('goodbye')

// 'hellogoodbye'

Append

Arguments

• str: String to append to each chunk.

var stream = sculpt.append('!!')

stream.on('data', console.log.bind(console))
stream.write('hello')
stream.write('world')

// 'hello!!world!!'

Prepend

Arguments

• str: String to prepend to each chunk.

var stream = sculpt.prepend('> ')

stream.pipe(process.stdout)
stream.write('hello\n')
stream.write('world')

// > hello
// > world

Replace

Arguments

• find: String or regex to search for in each chunk.
• replace: String or function to replace the found value with.

var stream = sculpt.replace('!', '?')

stream.pipe(process.stdout)
stream.write('hello! ')
stream.write('world ')
stream.write('goodbye!')

// 'hello? world goodbye?'

Join

Arguments

• str: A string to join each element in the chunk by.

This is intended to be used on arrays, but could work on any data type that has a join() method.

var stream = sculpt.join('|')

stream.pipe(process.stdout)
stream.write([1, 2, 3])
stream.write(['foo', 'bar'])

// '1|2|3foo|bar'

Invoke

Arguments

• methodName: A method to call on each chunk.
• args: Optional, arguments to pass to the named method

var stream = sculpt.invoke('toString')

stream.pipe(process.stdout)
stream.end(123)

// '123'

Split

Arguments

• str: A string to split each element in the chunk on.

This is intended to be used on strings (and create arrays), but could work on any data type that has a split() method.

var stream = sculpt.split('|')
var partNumber = 0
stream.on('data', function (part) {
  partNumber++
  console.log(partNumber, part)
})

stream.write('hi|bye|foo|bar')

// '1 hi'
// '2 bye'
// '3 foo'
// '4 bar'

Byte Length

Arguments

• length: Length in bytes for each output chunk

Each output chunk will be a buffer of length bytes, except the last chunk, which will be however many bytes are left over.

var stream = sculpt.byteLength(5)
stream.on('data', function (chunk) {
  console.log(chunk.toString())
})
stream.end('abcdefghijk')

// 'abcde'
// 'fghij'
// 'k'

Fork

Arguments

• stream: A writable stream that will also receive writes passed to this transform stream.

Errors from the forked stream are bubbled up to this transform stream.

var stream = sculpt.fork(process.stderr)

stream.pipe(process.stderr)
stream.write('hello world')

// 'hello world' is output to stdout and stderr

Tap

Arguments

• callback: A side effect function that is called with each chunk. It's return value is ignored and the chunk is propagated along the stream, unchanged.

var count = 0
var stream = tap(function (item) {
  if (item === 'bump') {
    count++
  }
})

stream.on('end', function () {
  console.log('Count is %d', count)
})

stream.write('bump')
stream.write('bump')
stream.write('hello')
stream.write('bump')

// 'Count is 3'

Pipes

Transform streams can be piped together. Let's say you have a file with song lyrics and you want to clean it up.

fs.createReadStream('./lyrics.txt')

  // Split into individual lines
  // The following streams will operate on one line at a time.
  .pipe(sculpt.split('\n'))

  // Remove trailing whitespace from each line
  .pipe(sculpt.replace(/\s+$/, ''))

  // Remove empty lines
  .pipe(sculpt.filter(function (line) {
    return line.length > 0
  }))

  // Bring back line breaks
  .pipe(sculpt.append('\n'))

  // Print the result
  .pipe(process.stdout)