fs.writeFile doesn't return a promise when not promisified explicitly

when I have code:

var Promise = require('bluebird');

var fs = Promise.promisifyAll(require('fs'));

fs.writeFile('./justATest.txt', 'hello', {}).then(function() {
    console.log("succesfulle written");
});

I get a

fs.writeFile('./justATest.txt', 'hello', {}).then(function() {
                                         ^
TypeError: Cannot call method 'then' of undefined    

It works when I promisify it explicitly:

var Promise = require('bluebird');
var writeFile = Promise.promisify(require('fs').writeFile);

writeFile('./justATest.txt', 'hello', {}).then(function() {
    console.log("succesfulle written");
});

So shouldn’t it work even in the first case?

[capaj]

@dzuluaga try

fs.writeFileAsync('./justATest.txt', 'hello', {}).then(function() {
    console.log("succesfully written");
});

after promisifying all. That should work according to the docs.

[dzuluaga]

Thanks @capaj. I was just posting the same finding. Thanks again!