Convert async code to promise

Question

I use the following code and I need to convert it to promise and at the end return object which contain the file configuration, how should I do that ?

 var Promise = require('bluebird'),
      glob = promisifyAll(require("glob")),
      fs = Promise.promisifyAll(require("fs"));

module.exports = {
    parse: function (configErr) {
    glob("folder/*.json", function (err, files) {
      if (err) {
        return configErr(new Error("Error to read json files: " + err));
      }
      files.forEach(function (file) {
        fs.readFileAsync(file, 'utf8', function (err, data) { // Read each file
          if (err) {
            return configErr(new Error("Error to read config" + err));
          }
          return JSON.parse(data);
        });
      })
    })

UPDATE -in the code I want to get json files from specific folder in my node project and parse the json content to object

You should explain what you are actually trying to do as well. — thefourtheye, Aug 02 '15 at 14:14
how about this: http://stackoverflow.com/questions/28521117/converting-async-code-to-q-promise-code-in-nodejs — EugenSunic, Aug 02 '15 at 14:16
@thefourtheye- I'll update my question ASAP with the data you ask — 07_05_GuyT, Aug 02 '15 at 14:17
@thefourtheye - this is all the code for this module parse json file to object — 07_05_GuyT, Aug 02 '15 at 14:20
Why convert it to promises? Most asyncness is used by the module itself. `configErr` seems to be the only external callback, pretty easy. — Rudie, Aug 02 '15 at 14:24
Look at the Promisification section of bluebird - https://github.com/petkaantonov/bluebird/blob/master/API.md#promisification — Ori Drori, Aug 02 '15 at 14:25
"*at the end return object which contain the file configuration*" - that won't work, as you're loading the files asynchronously. The best bet is to return a promise for the configuration. — Bergi, Aug 02 '15 at 14:32

Bergi · Accepted Answer · 2015-08-02T15:38:53.840

3

Promisified functions return promises, you should use those instead of passing callbacks into the invocation. Btw, your forEach loop does not work asynchronously, you should use a dedicated promise function for that.

 var Promise = require('bluebird'),
     globAsync = Promise.promisify(require("glob")),
     fs = Promise.promisifyAll(require("fs"));

module.exports.parse = function() {
    return globAsync("folder/*.json").catch(function(err) {
        throw new Error("Error to read json files: " + err);
    }).map(function(file) {
        return fs.readFileAsync(file, 'utf8').then(JSON.parse, function(err) {
            throw new Error("Error to read config ("+file+")" + err);
        });
    });
};

Then you can import this promise, and catch errors or use the array of parsed config objects by attaching callbacks to it via .then.

var config = require('config');
config.parse().then(function(cfg) { … }, function onConfigErr(err) { … })

edited Aug 02 '15 at 15:38

answered Aug 02 '15 at 14:58

Bergi

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Thanks I try it and I got error undefined is not a function in the .catch(function(err) { ,any idea? – 07_05_GuyT Aug 02 '15 at 15:02
@shopiaT: Please log the result of the `globAsync` call to see what it is. [Promisification](http://bluebirdjs.com/docs/api/promise.promisify.html) should work fine on `glob`. – Bergi Aug 02 '15 at 15:06
How should I log it ? – 07_05_GuyT Aug 02 '15 at 15:09
But how I got error when I run it ,Do you want me to change the code? – 07_05_GuyT Aug 02 '15 at 15:10
Yes, please use standard debugging techniques. If you don't want to point a debugger at node, edit the code and insert `console.log` statements where appropriate. – Bergi Aug 02 '15 at 15:11
I think I know what is the problem, assume that I want to call to this functionality parse(as my question post): function () { .... how should I call it ? can you please update the answer with it ? – 07_05_GuyT Aug 02 '15 at 15:16
Let us [continue this discussion in chat](http://chat.stackoverflow.com/rooms/84936/discussion-between-shopia-t-and-bergi). – 07_05_GuyT Aug 02 '15 at 15:17
I've removed the `parse` method from the module as it looked quite unnecessary. The files start to load when the module is loaded, and the results are exported as a promise. You can use that like `require('config').then(function(cfg) { … }, function(err) { … })` – Bergi Aug 02 '15 at 15:18

Convert async code to promise

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