Best ways to merge folders using nodejs, grunt or gulp - node.js

Question

I have two folders and I just want to merge them (overwriting BaseFolder files with ExtendedFolder ones when present)
Example:
BaseFolder
---main.js
---test.js
ExtendedFolder
---main.js
Result expected:
ResultFolder
---main.js (from ExtendedFolder)
---test.js (from BaseFolder)
I similar question has been asked but without a satisfying answer: Grunt. Programmatically merge corresponding files in parallel folders with concat

Answer 1

EDIT: I just realized my previous answer wouldn't work. I am posting new code.
If you just have two specified folders and want to merge their content, it would be pretty straightforward with gulp (this assumes that the folder names are known before and don't change):
var gulp = require('gulp');
gulp.task('moveBase',function(){
return gulp.src('BaseFolder/*')
.pipe(gulp.dest('ResultFolder/'));
});
gulp.task('moveExtended',['moveBase'],function(){
return gulp.src('ExtendedFolder/*')
.pipe(gulp.dest('ResultFolder/'));
});
gulp.task('mergeFolders',['moveBase','moveExtended']);
The files in BaseFolder having the same names as files in ExtendedFolder get overwritten.
The key here is the order of copying. First, copy the folder whose files should be overwritten in case of a conflict. You can split the copying into two tasks and take advantage of the dependency system - task moveExtended depends on moveBase which ensures that it will be copied later.

Answer 2

I was able to do exactly what I wanted using https://www.npmjs.org/package/event-stream
var gulp = require('gulp')
, es = require('event-stream');
gulp.task('web_dev', function () {
es.merge(gulp.src('./BaseFolder/**/*')
, gulp.src('./ExtendedFolder/**/*'))
.pipe(gulp.dest('out'));
});