JSPM – pull-reduction@1.0.1

Package Exports

pull-reduction

This package does not declare an exports field, so the exports above have been automatically detected and optimized by JSPM instead. If any package subpath is missing, it is recommended to post an issue to the original package (pull-reduction) to support the "exports" field. If that is not possible, create a JSPM override to customize the exports field for this package.

Readme

On an array:

var assert = require('assert')

assert([1, 2, 3, 4].reduce(function (a, b) { return a + b }) === 10)

In a pull-stream pipeline:

var reduction = require('pull-reduction')
var pull = require('pull-stream')

pull(
  pull.values([1, 2, 3, 4]),
  reduction(
    function add (reduced, current, callback) {
      callback(null, reduced + current)
    },
    function (error, reduced) {
      assert(error === null, 'no stream error')
      assert(reduced === 10, 'reduces to sum')
    }
  )
)

If both the source and the reduction call back synchronously, pull-reduction will loop, rather than recurse, to keep the stack short.

On an array:

assert(
  [0, 0, 0, 0, 0].reduce(function (a, b, index) {
    return a + index
  }, 100) === 110
)

In a pull-stream pipeline:

pull(
  pull.values([0, 0, 0, 0, 0]),
  reduction(
    // If the reducing function takes four arguments, it receives the
    // current index, as well.
    function add (reduced, current, index, callback) {
      callback(null, reduced + index)
    },
    // With three arguments, `reduction` sets an initial value.
    100,
    function (error, reduced) {
      assert(error === null, 'no stream error')
      assert(reduced === 110, 'reduces to sum of indices + initial')
    }
  )
)

Reductions can fail with errors:

pull(
  pull.values([1, 2, 3, 4, 5]),
  reduction(
    function fail (reduced, current, callback) {
      callback(new Error('reduction error'))
    },
    function (error, reduced) {
      assert(error.message === 'reduction error', 'aborts with error')
    }
  )
)