Node-fs-extra: Promise.promisifyAll doesn't work for some methods

[louwers]

Hi there!

Since it is mentioned in the README that fs-extra's methods can be promisified with bluebird's promisifyAll method, I figured out that I should report the following: not all methods seem to be promisified correctly with that method.

As far as I can tell, .readJson is one such method.

Using var fs = Promise.promisifyAll(require('fs-extra')) yields the following error upon evoking fs.readJson:

/path/node_modules/jsonfile/index.js:19
    callback(null, obj)
    ^
TypeError: undefined is not a function
    at /path/node_modules/jsonfile/index.js:19:5
    at fs.js:334:14
    at FSReqWrap.oncomplete (fs.js:95:15)

On the other hand, using var fs = require('fs') and later fs.readJson = Promise.promisify(fs.readJson) works fine for me. I therefore suggest warning users that some methods need to be promisified individually in order to work, if others are able to reproduce this problem, that is. Note that fs-extra-promise is also affected by this.

Note that I am using Promises in async/await functions with Babel, so there is a real possibility that those that are just using Promises with bluebird do not experience the same problem.

[jprichardson]

It's because promsifyAll appends Async to the method names.

See this snippet:

var Promise = require('bluebird')
var fs = require('fs-extra')
var fsp = Promise.promisifyAll(fs)
fsp.readJsonAsync('./package.json')
.then(function (obj) {
  console.dir(obj)
})
.catch(function (err) {
  console.error(err)
})

[jprichardson]

https://github.com/petkaantonov/bluebird/blob/master/API.md#promisepromisifyallobject-target--object-options---object

[louwers]

Thank you for enlightening me.
Lesson learned: RTFM.

[jprichardson]

It's ok, we've all been there :)