electron-wait-react.js

const net = require('net')
const port = process.env.PORT ? process.env.PORT - 100 : 5000

process.env.ELECTRON_START_URL = `http://localhost:${port}`

const client = new net.Socket()

let startedElectron = false
const tryConnection = () =>
  client.connect({ port: port }, () => {
    client.end()
    if (!startedElectron) {
      console.log('starting electron')
      startedElectron = true
      const exec = require('child_process').exec
      exec('yarn run electron')
    }
  })

tryConnection()

client.on('error', error => {
  setTimeout(tryConnection, 1000)
})