CODEWITHSUNDEEP
javascriptnode.jspromisefs
Deniz Ozger
Deniz Ozger

Reputation: 2623

Reading files in multiple directories, matching filenames with their data using Node and Promises

I have an array of directories.

var directories = ['/dir1', '/dir2'];

I want to read all files under these directories, and in the end have an object that matches filenames with their base64/utf8 data. In my case these files are images. The resulting object might look like:

var result = {
 '/dir1': {
  'file1': 'iVBORw0KGgoAAAANSUhEUgAAAOEAAADhCAIAAACx0UUtAAAAGXRFWHRTb2Z0d2FyZQBBZG9iZSBJbWF...',
  'file2': 'iVBORw0KGgoAAAANSUhEUgAAAOEAAADhCAIAAACx0UUtAAAAGXRFWHRTb2Z0d2FyZQBBZG9iZSBJbWF...'   
 }
}

I easily implemented this with a callback hell, but when I try with Promises, I'm not sure how to pass directory information, and filename to succeeding then() and map() functions.

In the example below I'm using Bluebird library:

const Promise = require('bluebird'),
  fs = Promise.promisifyAll(require('fs'));

var getFiles = function (dir) {
      return fs.readdirAsync(dir);
  };

Promise.map(directories, function(directory) {
    return getFiles(directory)
  }).map(function (files) {
    // which directory's files are these?
    return files;
  })

The next step would be iterating over files and reading their data.

I don't mind if answer is with ES6, Bluebird, or Q.

Upvotes: 3

Views: 2289

Answers (2)

Bergi
Bergi

Reputation: 665574

The easiest way with Bluebird would be to use props:

function getFiles(paths) { // an array of file/directory paths
    return Promise.props(paths.reduce(function (obj, path) {
        obj[path.split("/").pop()] = fs.statAsync(path).then(function (stat) {
            if (stat.isDirectory())
                return fs.readdirAsync(path).map(function (p) {
                    return path + "/" + p;
                }).then(getFiles);
            else if (stat.isFile())
                return fs.readFileAsync(path);
        }).error(function (e) {
            console.error("unable to read " + path + ", because: ", e.message);
            // return undefined; implied
        });
        return obj;
    }, {}));
}

Upvotes: 2

Lewis
Lewis

Reputation: 14926

I have no idea about Bluebird, but this is the ES6 Promise approach.

var fs = require('fs');
var directories = ['/dir1', '/dir2'];
var result = {};
Promise.all(directories.map(function(dir) {
  result[dir] = {};
  return new Promise(function(resolve, reject) {
    fs.readdir(dir, function(er, files) {
      if (er) {
        return reject(er);
      }
      resolve(files);
    });
  }).then(function(files) {
    return Promise.all(files.map(function(file) {
      return new Promise(function(resolve, reject) {
        fs.readFile(dir + '/' + file, function(er, data) {
          if (er) {
            return reject(er);
          }
          result[dir][file] = data.toString('base64');
          resolve();
        });
      });
    }));
  });
})).then(function() {
  console.log(result);
}).catch(function(er) {
  console.log(er);
});

Upvotes: 1

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