lazyLoad.ts

/**
 * Workaround to set up a handshake, lazy-loading by resolving a promise
 */
 
let settleReadyState = {}
let subprocess = {}

// following code outputs: Promise {<pending>} on console and sets
// settleReadyState = { resolve: ƒ, reject: ƒ}
// subprocess = {ready: Promise<pending>}

subprocess.ready = new Promise(
  (resolve, reject) => Object.assign(settleReadyState, { resolve, reject })
)

// following code outputs: subprocess = {ready: Promise<fulfilled>}
subprocess.once('message', () => {
  settleReadyState.resolve()
  subprocess.on('message', console.log);
})

// lazy-loading and sending message
subprocess.ready.then(
  () => subprocess.send({ hello: 'child' })}
)