Why doesn't elixir work in gulp?

Question

gulp.js

Hello, there is such a package.json:

{
  "name": "test",
  "version": "1.0.0",
  "main": "index.js",
  "license": "MIT",
  "dependencies": {
    "gulp": "^4.0.2",
    "gulp-stylus": "^2.7.0",
    "laravel-elixir-gulp-v4-compat": "^6.0.0-18"
  }
}

Gulpfile.js has the following content:

const elixir = require('laravel-elixir-gulp-v4-compat');

function defaultTask(cb) {
    elixir(function (mix) {
        mix.sass('./app.scss', './build/app.css');
    });
    cb();
}
exports.default = defaultTask

In the console output:

And the file build / app.css does not appear. I do not understand why it does not work, tell me please what could be the problem. Thank you in advance for your response.