Delayed Node.js response

webserver.js

// Storing response objects for delayed responses
const responseByMessage = {}

// A forked process that does some necessary heavy lifting
const worker  = require('child_process').fork(
  require('path').resolve('worker.js'), [],
  {stdio:['inherit', 'inherit', 'inherit', 'ipc']}
)

require('http').createServer(function (req, res) {
  if (req.url=='/') {
    // ...
  } else if (req.url=='/scenarios') {
    responseByMessage.scenarios = res
    worker.send({action:'scenarios'})
  }
}).listen(8080);

worker.on('message', msg => {
  switch (msg.action) {
    case 'scenarios':
      let res = responseByMessage.scenarios
      if (res) {
        res.writeHead(200, {'Content-Type':'application/json'})
        res.end(JSON.stringify(msg.data))
        delete responseByMessage.scenarios
      }
    break
  }
})

worker.js

if (process.send) {
  process.on('message', msg => {
    switch (msg.action) {
      case 'scenarios':
        process.send({action:'scenarios', data:buildScenarioList()})
      break;
    }
  })
}