Gulp sequential execution of same task on array of source files

A simplified version of my gulp file looks like this:

stylusFiles=[...];

gulp.task("stylus", function(done){
  global.stopOnError = true;
  stylusFiles.forEach((file) => {
    executeStylus(file.name, file.src, Date.now());
  });
  done();
});

javascFiles = [firstjs, secondjs];

gulp.task("firstcompile", function (done) {
  createBundle(firstjs);
  done();
});

gulp.task("secondcompile", function (done) {
  createBundle(secondjs);
  done();
});

gulp.task("compile", function(done) {
  setVersion();
  global.stopOnError = true;
  stylusFiles.forEach((file) => {
    executeStylus(file.name, file.src, Date.now());
  });

  createBundles(javascFiles);
  done();
});

gulp.task("seqcompile",
  gulp.parallel("stylus",
  gulp.series("firstcompile","secondcompile"), 
  function(done) {
    setVersion();
    global.stopOnError = true;
    done();
  }
));

Stylus compilation works in concurrent manner (output order != order of stylus files in code). If I run gulp on any single JS file, it works. The reason I try to force sequential execution is that gulp compile on the full set of JS files either crashes with an "out of heap memory" error (even using --max_old_stack_size=12000 on a 16 GB workstation) or runs indefinitely (>10 h) on the larger JS files (original size <=24 MB). However, the way it is written here in the example, gulp seqcompile is still not sequential, since output order != order of JS files in code, and on my remote instance, gulp still runs indefinitely (at least I have now had success on the 16 GB workstation).

1. How do I force sequential execution?
2. It would be nice to be able to write something like gulp.series(javascFiles).
3. I am not sure if setVersion is run only once before both stylus and js compilation, as it should.

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