Dynamic mapping for destinations in grunt.js - gruntjs

Question

I have a project with several sub folders that contain JavaScript files I want to concatenate. what would be the right way to configure them?
eg.
source: /modules/$modulename/js/*.js (several files)
dest: /modules/$modulename/js/compiled.js
So what I want to do is to compile js-files of an unknown/unconfigured count of subfolders ($modulename) into one file per subfolder.
Is this possible?
The following function (built after hereandnow78's instructions) does the job:
grunt.registerTask('preparemodulejs', 'iterates over all module directories and compiles modules js files', function() {
// read all subdirectories from your modules folder
grunt.file.expand('./modules/*').forEach(function(dir){
// get the current concat config
var concat = grunt.config.get('concat') || {};
// set the config for this modulename-directory
concat[dir] = {
src: [dir + '/js/*.js', '!' + dir + '/js/compiled.js'],
dest: dir + '/js/compiled.js'
};
// save the new concat config
grunt.config.set('concat', concat);
});
});
after that i put preparemodulejs before the concat job in my default configuration.

Answer 1

you will probably need to code your own task, where you iterate over your subfolders, and dynamically append to your concat configuration.
grunt.registerTask("your-task-name", "your description", function() {
// read all subdirectories from your modules folder
grunt.file.expand("./modules/*").forEach(function (dir) {
// get the current concat config
var concat = grunt.config.get('concat') || {};
// set the config for this modulename-directory
concat[dir] = {
src: ['/modules/' + dir + '/js/*.js', '!/modules/' + dir + '/js/compiled.js'],
dest: '/modules/' + dir + '/js/compiled.js'
};
// save the new concat configuration
grunt.config.set('concat', concat);
});
// when finished run the concatinations
grunt.task.run('concat');
});
run this with:
$ grunt your-task-name
this code is untested, but i think it should do your job.
HINT: you can put this code into an external file and include in your gruntfile if you want to keep your gruntfile small, e.g. put this into a file inside a tasks-directory:
module.exports = function(grunt) {
grunt.registerTask("your-task-name", "your description", function() {
...
});
};
and load in in your gruntfile:
grunt.loadTasks("./tasks");