eventmod-test.js

module.exports = function(config) {
  if(config.cli){
    /** Current Way:
    let onPlayerSandbox = config.engine.onPlayerSandbox;
    config.engine.onPlayerSandbox = function(sandbox, userId) {
      sandbox.test = function(){ return 'Hello World!' }
      return onPlayerSandbox(sandbox,userId)
    }
    **/
    // Proposed way
    config.cli.on('createSandbox',(event,sandbox)=>{
      sandbox.test = function(){ return 'Hello World!' }
    })
  }
  if(config.engine){
    // Normal way: (Not multimod firendly)
    /**
    config.engine.onProcessObject = function(object) {
        if(object.type == 'keeperLair') {
            return false; // This object will not be processed
        }
    }**/
    // Event based way: (More multimod friendly)
    config.engine.on('processObject',(event, object, roomObjects, roomTerrain, gameTime, roomInfo, objectsUpdate, usersUpdate)=>{
      if(object.type == 'keeperLair'){
        event.preventDefault() // Prevents default handler from running
        event.returnValue = false
      }
   })
  }
}

eventmod.js

const { EventEmitter } = require('events')

module.exports = function(config) {
  if(config.__eventmod_hooked) return
  config.__eventmod_hooked = true
  for (let modName in config) {
    let mod = config[modName]
    let ee = new EventEmitter()
    config[modName] = new Proxy(mod,{
      get: (target,name)=>ee[name] || target[name]
    })
    let hooked = {}
    ee.on('newListener',(eventName,listener)=>{
      // This allows us to hook the event on first listener
      if(hooked[eventName]) return
      hooked[eventName] = true
      console.log('Hooking event',eventName)
      let name = `on${eventName.slice(0,1).toUpperCase}${eventName.slice(1)}`
      let orig = mod[name]
      mod[name] = function(...args) {
        let def = true
        let event = { returnValue: null, preventDefault: ()=>def=false }
        ee.emit(event,eventName, ...args)
        if(def) orig(...args)
        return event.returnValue
      }
    })
  }
}

/* 
*/