gf-event-store/src/event-bus.js

a lightweight state maneger

class GfEventBus {
  constructor() {
    this.eventBus = {}
  }

  on(eventName, eventCallback, thisArg) {
    if (typeof eventName !== "string" || !eventName) {
      throw new TypeError(
        "the event name must be string type and event name not be null string"
      )
    }

    if (typeof eventCallback !== "function") {
      throw new TypeError("the eventCallbackFunction must be function type")
    }

    let subscribers = null
    if (!this.eventBus[eventName]) {
      this.eventBus[eventName] = []
    }
    subscribers = this.eventBus[eventName]
    subscribers.push({ eventCallback, thisArg })
    subscribers = null
    return this
  }

  off(eventName, eventCallback) {
    if (typeof eventName !== "string" || !eventName) {
      throw new TypeError(
        "the event name must be string type and event name not be null string"
      )
    }
    if (!(eventName in this.eventBus)) {
      console.log("There is no function for this eventName")
      return
    }
    //如果第二个参数是布尔类型的值，且为true，则清空所有注册事件
    if (typeof eventCallback === "boolean" && eventCallback === true) {
      this.eventBus[eventName] = []
      delete this.eventBus[eventName]
      return
    }
    if (typeof eventCallback !== "function") {
      throw new TypeError("the eventCallbackFunction must be function type")
    }

    let handlers = this.eventBus[eventName]
    let newHandlers = null
    if (handlers) {
      newHandlers = [...handlers]
      for (const handlerItem of newHandlers) {
        if (handlerItem.eventCallback === eventCallback) {
          let index = handlers.indexOf(handlerItem)
          handlers.splice(index, 1)
        }
      }
    }
    if (handlers.length === 0) {
      delete this.eventBus[eventName]
    }
    newHandlers = null

    return this
  }

  once(eventName, eventCallback, thisArg) {
    if (typeof eventName !== "string" || !eventName) {
      throw new TypeError(
        "the event name must be string type and event name not be null string"
      )
    }
    if (typeof eventCallback !== "function") {
      throw new TypeError("the eventCallbackFunction must be function type")
    }

    const onceEventCallback = (...payload) => {
      eventCallback.call(thisArg, ...payload)
      this.off(eventName, true)
    }
    onceEventCallback.eventCallback = eventCallback
    return this.on(eventName, onceEventCallback, thisArg)
  }

  emit(eventName, ...payload) {
    if (typeof eventName !== "string" || !eventName) {
      throw new TypeError(
        "the event name must be string type and event name not be null string"
      )
    }

    // if (!(eventName in this.eventBus)) {
    //   console.log("There is no function for this eventName")
    //   return
    // }

    if (!this.eventBus[eventName] || this.eventBus[eventName].length === 0) {
      return
    }
    this.eventBus[eventName].forEach((handleItem) => {
      handleItem.eventCallback.call(handleItem.thisArg, ...payload)
      if (!this.eventBus[eventName]) return
    })
    return this
  }
}

module.exports = GfEventBus