callexistinggrunttasksfromothergruntfileAdapterObserver.js

  grunt.registerTask('taskname', 'My awesome task', function () {
    var done = this.async();
    // Epic hacks
    var grunt = require('grunt');
    grunt.task.init = function() {};
    grunt.initConfig({
      compress: {
        target: {
          options: {
            archive: '../app.zip'
          },
          files: [
            { src: ['**'] }
          ]
        }
      }
    });

    // you might have to change this, this might be required for `loadNpmTasks`
    var cwd = process.cwd();
    process.chdir(__dirname + '/..');
    grunt.loadNpmTasks('grunt-contrib-compress');
    process.chdir(cwd);

    // Finally run the tasks, with options and a callback when we're done
    grunt.tasks(['compress'], {}, function() {
      // compress done running  
    });
    
  });