ES6 Promise version .vm

[Kailang]

Trying to add a ES6 Promise version of the .mv function.

Here's the draft:

        mvPromise: function(path) {
          return new Promise((resolve, reject) => {
            let fstream = fs.createWriteStream(path);

            streamifier.createReadStream(buf).pipe(fstream);

            fstream.on('error', function(error) {
              reject(error);
            });

            fstream.on('close', function() {
              resolve();
            });
          });
        }

This should be appended after the .vm definition in let newFile.

Any suggestions? If this looks good, I'll create a pull request with a test.

[richardgirges]

Hey this looks good, but I'm wondering if we can just update the existing mv method instead. If a callback is passed in, it executes a callback. Otherwise, it returns a promise. Make sense?

[Kailang]

Yeah, of course, why not?

        mv: function(path, callback) {
          if (callback) {
            let fstream = fs.createWriteStream(path);

            streamifier.createReadStream(buf).pipe(fstream);

            fstream.on('error', error => callback(error));
            fstream.on('close', () => callback(null));
          } else {
            return new Promise((resolve, reject) => {
              let fstream = fs.createWriteStream(path);

              streamifier.createReadStream(buf).pipe(fstream);

              fstream.on('error', error => reject(error));
              fstream.on('close', () => resolve(null));
            });
          }
        }

And if you dislike lambda expression...

        mv: function(path, callback) {
          if (callback) {
            let fstream = fs.createWriteStream(path);

            streamifier.createReadStream(buf).pipe(fstream);

            fstream.on('error', function (error) {
              callback(error);
            });
            
            fstream.on('close', function () {
              callback(null);
            });
          } else {
            return new Promise((resolve, reject) => {
              let fstream = fs.createWriteStream(path);

              streamifier.createReadStream(buf).pipe(fstream);

              fstream.on('error', function (error) {
                reject(error);
              });

              fstream.on('close', function () {
                resolve(null);
              });
            });
          }
        }

Plus a way to reduce one level of indention:

        mv: function(path, callback) {
          if (!callback) {
            return new Promise((resolve, reject) => {
              let fstream = fs.createWriteStream(path);

              streamifier.createReadStream(buf).pipe(fstream);

              fstream.on('error', error => reject(error));
              fstream.on('close', () => resolve(null));
            });
          }
          
          let fstream = fs.createWriteStream(path);

          streamifier.createReadStream(buf).pipe(fstream);

          fstream.on('error', error => callback(error));
          fstream.on('close', () => callback(null));
        }

And the old fashion:

        mv: function(path, callback) {
          if (!callback) {
            return new Promise((resolve, reject) => {
              let fstream = fs.createWriteStream(path);

              streamifier.createReadStream(buf).pipe(fstream);

              fstream.on('error', function (error) {
                reject(error);
              });

              fstream.on('close', function () {
                resolve(null);
              });
            });
          }

          let fstream = fs.createWriteStream(path);

          streamifier.createReadStream(buf).pipe(fstream);

          fstream.on('error', function (error) {
            callback(error);
          });

          fstream.on('close', function () {
            callback(null);
          });
        }