@gar/promisify

Promisify an entire object or class instance

This module leverages es6 Proxy and Reflect to promisify every function in an object or class instance.

It assumes the callback that the function is expecting is the last parameter, and that it is an error-first callback with only one value, i.e. (err, value) => .... This mirrors node's util.promisify method.

In order that you can use it as a one-stop-shop for all your promisify needs, you can also pass it a function. That function will be promisified as normal using node's built-in util.promisify method.

node's custom promisified functions will also be mirrored, further allowing this to be a drop-in replacement for the built-in util.promisify.

Examples

Promisify an entire object

const promisify = require('@gar/promisify')

class Foo {
  constructor (attr) {
    this.attr = attr
  }

  double (input, cb) {
    cb(null, input * 2)
  }

const foo = new Foo('baz')
const promisified = promisify(foo)

console.log(promisified.attr)
console.log(await promisified.double(1024))

Promisify a function

const promisify = require('@gar/promisify')

function foo (a, cb) {
  if (a !== 'bad') {
    return cb(null, 'ok')
  }
  return cb('not ok')
}

const promisified = promisify(foo)

// This will resolve to 'ok'
promisified('good')

// this will reject
promisified('bad')