Yes it does.
In this page of the docs:
https://laravel-mix.com/docs/6.0/mixjs
It says that mix will Compile the latest JavaScript syntax for you.
And this phrase is linked to:
https://babeljs.io/docs/en/babel-preset-env
Depending on what feature you need, you might need to add additional plugins, but babel-preset-env should include all Stage 3 features from JavaScript.