Deferral components allow your function to specify cleanup operations that must be run once your function is completed. These cleanup operations will be executed whether the function completes or errors out.

You can wrap your function with a deferral using Deferral.fromAsync(). The first argument to your function will be the defer() function which allows you to pass callbacks to execute for cleanup.

• Will be executed in reverse order.
• If one errors out, the rest will not be executed.
• If it returns a promise, the deferral will wait for the promise to resolve before exiting your function.
• Other than promises, all return values from deferred functions are ignored.

import { Deferral } from 'rsxjs'
import { open, close } from 'mz/fs'

// this function will do make sure the file is closed
// even if it errors out
const doStuff = Deferral.fromAsync(async function (defer, file) {
  const fd = await open(file)
  defer(() => close(fd))

  // do things with the file or just die, whatever
  throw new Error('DIE!')
})