SSE auto-revive connection

ImmortalSSE.js

export const ImmortalSSE = url => {
  let url
  let instance
  let listeners = []

  const timeout = 2000

  const create = () => {
    if (url == undefined) {
      return
    }

    return new EventSource(url)
  }

  const addEventListener = (name, callback) => {
    let source = instance()
    source.addEventListener(name, callback, false)
    source.onerror = function(e) {
        // EventSource failed
        source.addEventListener(name, callback, false)
    }

    return source
  }

  const reListen = () => {
    listeners.map((item) => {
      addEventListener(item.name, item.callback)
    })
  }

  const instance = () => {
    // instantiate
    if (instance != undefined) {
      return instance
    }

    // create new
    instance = create()

    // hearbeat
    setInterval(() => {
      switch (instance.readyState) {
      case instance.CONNECTING:
        // wait and connecting
        break;
      case instance.CLOSED:
        // re-create new when close
        instance = create()

        // re listen
        reListen()

        break;
      }
    }, timeout)

    return instance
  }

  const addListener = (name, callback) => {
    // sse add event listeners
    let source = addEventListener(name, callback)

    // for refresh purposes
    listeners.push({
      name,
      callback,
    })

    return source
  }

  return {
    url,
    addListener,
  }
}