Set up your local environment
JavaScript could run in the browser, served from a file. Running it from a webserver, will have several advantages, e.g. access to objects in the code you are writing. We also need a webserver to be able to fetch content from other domains.
Setting up a webserver
Set up a local webserver of your choice
To speedup and facilitate your setup, you can use tools like MAMP
Create a Folder for you application
DNS or not?
Up to you, to serve the files from localhost / 127.0.0.1 or from a local DNS.
My preference is to use the .hosts file to setup a local domain.
Note
Remember to setup a local SSL certificate, to be able to run secure
Testing the setup
Add an index.html to the root of your folder, and insert "Hello world"
Browse to the webserver / folder to see
You now have a working website on a local webserver!