kefir/src/one-source/skip-duplicates.js

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

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

const mixin = {
  _init({fn}) {
    this._fn = fn
    this._prev = NOTHING
  },

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

  _handleValue(x) {
    const fn = this._fn
    if (this._prev === NOTHING || !fn(this._prev, x)) {
      this._prev = x
      this._emitValue(x)
    }
  },
}

const S = createStream('skipDuplicates', mixin)
const P = createProperty('skipDuplicates', mixin)

const eq = (a, b) => a === b

export default function skipDuplicates(obs, fn = eq) {
  return new (obs._ofSameType(S, P))(obs, {fn})
}