What is it you're trying to manage with "custom dependencies"?
(I'm presuming you mean "custom objects")
You can either create them manually in SDF (no thanks), or create them in the UI and import them to your project. If you're talking about moving them between accounts you can move them in bundles too.
If you mean something else, you're going to need to expand on "_manage these with SDF_". Or wait on another response 😉
Your question about "const" is puzzling, it's native javascript not specific to SuiteScript, you might need to explain what it is you mean or want to know.
JSDOC.. entries are there if you use a decent IDE and the NetSuite plugin when you create a script, so emphatically yes you can use JSDOC, but is there something specific you have in mind?
(btw try searching this channel for "jsdoc" 😉 )