kefir/src/one-source/scan.js

Reactive Programming library for JavaScript inspired by Bacon.js and RxJS with focus on high performance and low memory usage

import {createProperty} from '../patterns/one-source'
import {ERROR, NOTHING} from '../constants'

const P = createProperty('scan', {
  _init({fn, seed}) {
    this._fn = fn
    this._seed = seed
    if (seed !== NOTHING) {
      this._emitValue(seed)
    }
  },

  _free() {
    this._fn = null
    this._seed = null
  },

  _handleValue(x) {
    const fn = this._fn
    if (this._currentEvent === null || this._currentEvent.type === ERROR) {
      this._emitValue(this._seed === NOTHING ? x : fn(this._seed, x))
    } else {
      this._emitValue(fn(this._currentEvent.value, x))
    }
  },
})

export default function scan(obs, fn, seed = NOTHING) {
  return new P(obs, {fn, seed})
}