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0.4.0 • Public • Published

Code Style for css-blocks and OptiCSS

This project adheres to the following conventions for code and its style. These conventions govern the code that runs during build-time. There are separate conventions for code intended to run in the browser.

Node Support Policy

Starting with Node 8, css-blocks, OptiCSS and related projects will support all Active LTS releases of Node. Once a node version moves into "Maintenance LTS" we reserve the right to drop support for it with the next minor release. Our projects are configured to set the node engine version in their package.json, so such releases will not regress for projects using older versions of node — but bug fixes and new features may not be released.

The exception to this is that critical security patches will be released for versions of our software to support projects using Node that remains in the Maintenance LTS mode.

Code Style

Specific Lint rules ran are not covered here. The source of truth is found in the configuration files below. Not all code style can be linted, here's what else you need to know:

  1. Code is written in TypeScript and transpiled to the newest version of ES Modules that are supported by our Node Support Policy (see above).
  2. All TypeScript code will use this project's configuration files where possible.
  3. Linting must be performed as part of yarn test for every node package.
  4. All code is compiled with TypeScript's strictest settings enabled and any new strictness options are enabled with each TypeScript release.
  5. We prefer for ... of loops for iteration.
  • forEach should only be used to apply an existing function to values in an array. Never use a local function with forEach.
  • If an object needs to provide a way to iterate over values, we prefer using a generator to taking a callback. This works better with for ... of loops.
  1. Avoid any. There are very few times it's necessary. We use the type whatever from @opticss/util to express very generic values without introducing the infectious semantics of any. Exceptions:
    • Using a value from library that has a very complex type for which types are not available or are not good enough. If possible, declare a local interface for the aspects of the library that we use. If any is needed, declare a type alias to any for that library and disable the lint rule for that line.
    • In very rare cases, casting through any is required to convince the type checker that a value will have the type you say it will have. More often than not, if the type checker says you can't cast to a value, it's right.

Test Code Style

Test code is linted like source code. Exceptions and Additions to those rules are listed here:

  1. Testing is done with ts-mocha, chai for assertions.
  2. Do not use "bdd-style" assertions (e.g. expect/should) for tests.
  3. Tests that use randomization or fuzzing to test a feature must include information in the output or error that makes it easy to reproduce the error either by seeding the random number generator or by including the actual values used in the error message.
  4. Integration testing is preferred to unit tests so that tests are robust against internal refactors.
  5. When unit testing, there is a preference for adding internal APIs to real objects over using mocks/stubs or other tools to inspect that a test had the expected outcomes to its unit and to the units it interacts with.


This project recommends the use of Visual Studio Code and includes configuration for integration with it to enhance the IDE experience with the tooling choices of the project and makes things like interactive debugging work easily while running the tests.

Shared Configuration Files

  • configs/tslint.interactive.json - These lints affect the way code is written and usually can't be fixed automatically. They are well-suited to be ran interactively while you develop. If you use VSCode, our provided configuration files will automatically be set up to run only these lints while you're writing code.
  • configs/tslint.cli.json - Lints that are best to run from the CLI after tests pass or before commit. Usually these can be fixed automatically by running lerna run lintfix. Automated fixers aren't perfect, so we recommend running the code after staging a commit so you can see what it did by running a git diff or with git add -p. When you run yarn test on a package or lerna run test on the repo, these lints will be used. This lint configuration file inherits from tslint.interactive.json.
  • configs/tslint.release.json - These lints perform sanity checks against code that is about to be released or checked in. These lints would be annoying under normal development workflows and so they're not included. This lint configuration file inherits from tslint.interactive.json. and rule customization for test code. This configuration does not extend any other configuration files. It is meant to be combined with the others for tests.


npm i @opticss/code-style

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