elixir style stream

stream.js

class Stream {
  constructor (collection) {
    this.collection = collection
    this.transformations = []
    this.acc = []
  }

  run () {
    let acc = this.acc
    let i = -1

    while (++i < this.collection.length) {
      let item = this.collection[i]

      this.transformations.forEach(transformFn => {
        if (typeof item === 'undefined') return

        if(transformFn.length == 2) {
          acc = transformFn(acc, item)
        } else {
          item = transformFn(item)
        }
      })
    }
    return acc
  }

  reduce (reducerFn, acc) {
    this.transformations.push(reducerFn)
    this.acc = acc
    return this
  }

  reverse () {
    this.enum.reverse()
    return this
  }

  map (mapperFn) {
    this.transformations.push(mapperFn)
    return this
  }

  filter (predicate) {
    const transform = item => predicate(item) ? item : undefined
    this.transformations.push(transform)
    return this
  }

  reject (predicate) {
    const transform = item => predicate(item) ? undefined : item
    this.transformations.push(transform)
    return this
  }
}
/*
To use:

s = new Stream ([1,2,3])

s.map((item) => item + 1)
 .filter((item) => item % 2 === 0)
 .reduce((agg, item) => agg + item, 0)
 .run()
*/