Course project

A helper library for the JSON of one product.

A small library of helper functions that makes writing check rules easier for other users, mainly by making it simpler and safer to read properties from the product's JSON. We build it for one product during the course; its structure should make the next products easy to add.

How it grows

Session	What we add
5. Functions	compareVersions(a, b) and versionBelow(a, b) - compare version strings
6. Objects	get(doc, path, fallback) - safe access to deep paths; the path as a string or an array (for keys with dots)
7. Array methods	kickoff: your own repository, a chosen product, sample documents, library.js; helpers that group a list of records and build an index
8. Strings, regex, dates	normalise versions in any format; parse dates and keys with a regular expression
9. JSON, modules, errors	the library as a CommonJS module; a local runner that runs a rule on a folder of sample documents with a fake emit; clear errors for bad input
10. Tests, types, review	tests with node:test; JSDoc types for the product's JSON; a README; presentation and code review

Deliverables

1. A CommonJS module for the product (<product>.js, or library.js) with documented helpers.
2. Tests with node:test on anonymised sample documents.
3. Two or three existing rules rewritten with the library.
4. A README with examples for other users.
5. JSDoc types (@typedef) for the product's JSON, checked with // @ts-check.

The minimum for the review: items 1, 2 and one rewritten rule. Items 3 - 5 can grow after the course.

The repository

A suggested layout (lecture 7 sets it up, lectures 9 and 10 fill it):

my-library/
|-- library.js            the helpers (module.exports = { ... })
|-- rules/                rules rewritten with the library
|   `-- chk-0211.js
|-- samples/              anonymised sample documents, one JSON file each
|-- run-rule.js           runs a rule on every sample, with a fake emit (lecture 9)
|-- test/                 tests with node:test (lecture 10)
|   `-- library.test.js
|-- README.md             what the helpers do, with examples
`-- package.json

Choices to make

Which product comes first, and which helpers are needed most. Collect examples of rules that are hard to write today.