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3.16 Writing Modules

• https://gist.github.com/substack/5075355

My thoughts on writing tiny reusable modules that each do just one thing. These notes were adapted from an email I recently sent.

If some component is reusable enough to be a module then the maintenance gains are really worth the overhead of making a new project with separate tests and docs. Splitting out a reusable component might take 5 or 10 minutes to set up all the package overhead but it’s much easier to test and document a piece that is completely separate from a larger project. When something is easy, you do it more often.

I’ve observed the biggest gains for splitting something out into a separate module when I’m completely stuck mucking around in a larger application. When I isolate the problem down to the scope of a small module, it’s much easier to see how that small piece fits in with the greater application objective.

Another technique is to pick tools and approaches that don’t involve a lot of boilerplate in the first place. My usual flow for writing a new module is:

1. hack up some tiny (<10 line) example file that does just enough to start experimenting with the api
2. start fleshing out an index.js file required by the example file
3. make incremental changes to the index file to get the example further along, updating the example as necessary to reflect changes
4. once the example pretty much works, copy it into test/
5. ‘npm install tap‘ or ‘npm install tape‘ for modules I want to test in the browser. I like simple, imperative tests that I can adapt from simple examples.
6. add some assertions around the example code
7. ‘pkginit‘ (https://github.com/substack/pkginit) to generate a package.json (or you could just use ‘npm init‘)
8. copy the example file into a readme.markdown since I really like when packages have code in their readmes when I’m looking for modules to use
9. add a blurb at the top of the readme.markdown, document the methods (there are only a few to document usually), add a license and install instructions
10. create a github repo
11. add travis and/or testling-ci github hooks as appropriate
12. ‘git push‘ and ‘npm publish‘

With practice, I run through all these steps very quickly now. Not all of these are strictly necessary and sometimes I’ll skip a step but this is mostly the procedure I use for new modules.

As much as possible, I try to build large-scale projects using lots of tiny modules so I just repeat this process whenever I need some reusable component that doesn’t yet exist in quite the form I need it to exist. As more modules are published to npm I expect I won’t need to write so many modules but there will always be room for new stuff.

When applications are done well, they are just the really application-specific, brackish residue that can’t be so easily abstracted away. All the nice, reusable components sublimate away onto github and npm where everybody can collaborate to advance the commons.