kefir/src/observable.js

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

import {extend} from './utils/objects'
import {VALUE, ERROR, ANY, END} from './constants'
import {Dispatcher, callSubscriber} from './dispatcher'
import {findByPred} from './utils/collections'

function Observable() {
  this._dispatcher = new Dispatcher()
  this._active = false
  this._alive = true
  this._activating = false
  this._logHandlers = null
  this._spyHandlers = null
}

extend(Observable.prototype, {
  _name: 'observable',

  _onActivation() {},
  _onDeactivation() {},

  _setActive(active) {
    if (this._active !== active) {
      this._active = active
      if (active) {
        this._activating = true
        this._onActivation()
        this._activating = false
      } else {
        this._onDeactivation()
      }
    }
  },

  _clear() {
    this._setActive(false)
    this._dispatcher.cleanup()
    this._dispatcher = null
    this._logHandlers = null
  },

  _emit(type, x) {
    switch (type) {
      case VALUE:
        return this._emitValue(x)
      case ERROR:
        return this._emitError(x)
      case END:
        return this._emitEnd()
    }
  },

  _emitValue(value) {
    if (this._alive) {
      this._dispatcher.dispatch({type: VALUE, value})
    }
  },

  _emitError(value) {
    if (this._alive) {
      this._dispatcher.dispatch({type: ERROR, value})
    }
  },

  _emitEnd() {
    if (this._alive) {
      this._alive = false
      this._dispatcher.dispatch({type: END})
      this._clear()
    }
  },

  _on(type, fn) {
    if (this._alive) {
      this._dispatcher.add(type, fn)
      this._setActive(true)
    } else {
      callSubscriber(type, fn, {type: END})
    }
    return this
  },

  _off(type, fn) {
    if (this._alive) {
      let count = this._dispatcher.remove(type, fn)
      if (count === 0) {
        this._setActive(false)
      }
    }
    return this
  },

  onValue(fn) {
    return this._on(VALUE, fn)
  },
  onError(fn) {
    return this._on(ERROR, fn)
  },
  onEnd(fn) {
    return this._on(END, fn)
  },
  onAny(fn) {
    return this._on(ANY, fn)
  },

  offValue(fn) {
    return this._off(VALUE, fn)
  },
  offError(fn) {
    return this._off(ERROR, fn)
  },
  offEnd(fn) {
    return this._off(END, fn)
  },
  offAny(fn) {
    return this._off(ANY, fn)
  },

  observe(observerOrOnValue, onError, onEnd) {
    const _this = this
    let closed = false

    const observer =
      !observerOrOnValue || typeof observerOrOnValue === 'function'
        ? {value: observerOrOnValue, error: onError, end: onEnd}
        : observerOrOnValue

    const handler = function(event) {
      if (event.type === END) {
        closed = true
      }
      if (event.type === VALUE && observer.value) {
        observer.value(event.value)
      } else if (event.type === ERROR && observer.error) {
        observer.error(event.value)
      } else if (event.type === END && observer.end) {
        observer.end(event.value)
      }
    }

    this.onAny(handler)

    return {
      unsubscribe() {
        if (!closed) {
          _this.offAny(handler)
          closed = true
        }
      },
      get closed() {
        return closed
      },
    }
  },

  // A and B must be subclasses of Stream and Property (order doesn't matter)
  _ofSameType(A, B) {
    return A.prototype.getType() === this.getType() ? A : B
  },

  setName(sourceObs /* optional */, selfName) {
    this._name = selfName ? `${sourceObs._name}.${selfName}` : sourceObs
    return this
  },

  log(name = this.toString()) {
    let isCurrent
    let handler = function(event) {
      let type = `<${event.type}${isCurrent ? ':current' : ''}>`
      if (event.type === END) {
        console.log(name, type)
      } else {
        console.log(name, type, event.value)
      }
    }

    if (this._alive) {
      if (!this._logHandlers) {
        this._logHandlers = []
      }
      this._logHandlers.push({name: name, handler: handler})
    }

    isCurrent = true
    this.onAny(handler)
    isCurrent = false

    return this
  },

  offLog(name = this.toString()) {
    if (this._logHandlers) {
      let handlerIndex = findByPred(this._logHandlers, obj => obj.name === name)
      if (handlerIndex !== -1) {
        this.offAny(this._logHandlers[handlerIndex].handler)
        this._logHandlers.splice(handlerIndex, 1)
      }
    }

    return this
  },

  spy(name = this.toString()) {
    let handler = function(event) {
      let type = `<${event.type}>`
      if (event.type === END) {
        console.log(name, type)
      } else {
        console.log(name, type, event.value)
      }
    }
    if (this._alive) {
      if (!this._spyHandlers) {
        this._spyHandlers = []
      }
      this._spyHandlers.push({name: name, handler: handler})
      this._dispatcher.addSpy(handler)
    }
    return this
  },

  offSpy(name = this.toString()) {
    if (this._spyHandlers) {
      let handlerIndex = findByPred(this._spyHandlers, obj => obj.name === name)
      if (handlerIndex !== -1) {
        this._dispatcher.removeSpy(this._spyHandlers[handlerIndex].handler)
        this._spyHandlers.splice(handlerIndex, 1)
      }
    }
    return this
  },
})

// extend() can't handle `toString` in IE8
Observable.prototype.toString = function() {
  return `[${this._name}]`
}

export default Observable