A single value emitter

raj-emitter.js

exports.createEmitter = function createEmitter ({ shouldPrime, initialValue }) {
  let currentValue = initialValue
  let listeners = []

  return {
    emit: value => () => {
      currentValue = value
      listeners.forEach(listener => listener(currentValue))
    },

    subscribe () {
      let listener
      return {
        effect (dispatch) {
          listener = dispatch
          listeners.push(listener)
          if (shouldPrime) {
            listener(currentValue)
          }
        },
        cancel () {
          listeners = listeners.filter(l => l !== listener)
        }
      }
    }
  }
}