kefir/src/one-source/throttle.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 now from '../utils/now'

const mixin = {
  _init({wait, leading, trailing}) {
    this._wait = Math.max(0, wait)
    this._leading = leading
    this._trailing = trailing
    this._trailingValue = null
    this._timeoutId = null
    this._endLater = false
    this._lastCallTime = 0
    this._$trailingCall = () => this._trailingCall()
  },

  _free() {
    this._trailingValue = null
    this._$trailingCall = null
  },

  _handleValue(x) {
    if (this._activating) {
      this._emitValue(x)
    } else {
      let curTime = now()
      if (this._lastCallTime === 0 && !this._leading) {
        this._lastCallTime = curTime
      }
      let remaining = this._wait - (curTime - this._lastCallTime)
      if (remaining <= 0) {
        this._cancelTrailing()
        this._lastCallTime = curTime
        this._emitValue(x)
      } else if (this._trailing) {
        this._cancelTrailing()
        this._trailingValue = x
        this._timeoutId = setTimeout(this._$trailingCall, remaining)
      }
    }
  },

  _handleEnd() {
    if (this._activating) {
      this._emitEnd()
    } else {
      if (this._timeoutId) {
        this._endLater = true
      } else {
        this._emitEnd()
      }
    }
  },

  _cancelTrailing() {
    if (this._timeoutId !== null) {
      clearTimeout(this._timeoutId)
      this._timeoutId = null
    }
  },

  _trailingCall() {
    this._emitValue(this._trailingValue)
    this._timeoutId = null
    this._trailingValue = null
    this._lastCallTime = !this._leading ? 0 : now()
    if (this._endLater) {
      this._emitEnd()
    }
  },
}

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

export default function throttle(obs, wait, {leading = true, trailing = true} = {}) {
  return new (obs._ofSameType(S, P))(obs, {wait, leading, trailing})
}