CYF ESLint Configuration

A standard ESLint configuration for all CYF examples/projects.

Versioning

This configuration uses SemVer, interpreted as follows:

• Patch release (x.y.z -> x.y.z+1): bugfixes and tooling updates mean that code that previously passed linting should continue to pass after the update.

• Minor release (x.y.z -> x.y+1.0): a change to an existing rule means that code that previously failed linting may now pass, or a new configuration means that code that previously passed linting should continue to pass.

• Major release (x.y.z -> x+1.0.0): a new rule, or a change to an existing rule, means that code that previously passed linting will not pass any more.

Please bear these definitions in mind when reporting any bugs.

Usage

Install this package along with ESLint itself:

npm install --save-dev eslint @codeyourfuture/eslint-config-standard

Then create an ESLint config file and add this config:

const cyfConfig = require("@codeyourfuture/eslint-config-standard");

module.exports = [cyfConfig];

or using ES module syntax:

import cyfConfig from "@codeyourfuture/eslint-config-standard";

export default [cyfConfig];

Alternatively, for a slightly more permissive set of rules, you can use @codeyourfuture/eslint-config-standard/lax.

.eslintrc

If you have not yet migrated to the newer ESLint "flat config", you can apply these rules to the deprecated config using "extends":

{
  "extends": ["@codeyourfuture/standard"]
}

Principles

1. Errors only - don't teach trainees to ignore any output, all rules should either be "error" or "off"
2. Maximise consistency - where there are options (e.g. braces for single-line statements, parentheses around arrow function parameters), be consistent with the non-optional cases
3. Minimise change set size - keep commits small so trainees can focus on the important changes

Rules

This config starts from js.configs.recommended then adds the following rules:

| Configuration| Rule | Setting | Principles/rationale | |---|---|---|---| | standard, lax | arrow-parens | | 2, 3 | | standard, lax | brace-style | "1tbs", { "allowSingleLine": false } | | | standard, lax | comma-dangle | "always-multiline" | 3 | | standard, lax | curly | | 2 | | standard | indent | "tab", { "SwitchCase": 1 } | Tabs are more accessible | | standard | linebreak-style | "unix" | | | standard, lax | no-trailing-spaces | | | | standard, lax | no-unused-vars | { "ignoreRestSiblings": true } | | | standard, lax | no-var | | Stick with let and const for more predictable behaviour | | standard, lax | object-curly-spacing | "always" | | | standard, lax | operator-linebreak | "before" | | | standard, lax | quotes | "double", { "avoidEscape": true, "allowTemplateLiterals": false } | More likely to need ' inside a string than " | | standard, lax | semi | | Trainees shouldn't have to memorise the ASI rules |

Development

You can clone this repo and run npm install to install the development dependencies. Two scripts are provided:

• lint: uses the version of ESLint installed as a dev dependency to lint index.js against its own rules.

• test:examples: runs bin/examples.sh to test the configuration against the pass.js and fail.js examples in examples/. pass.js contains code that should pass linting according to the configuration, fail.js contains code that should fail linting.

• test:install: runs bin/test.sh to create a package, installs ESLint (version defined by the required environment variable ESLINT_VERSION) and the current version of this configuration, then checks that there are no version conflicts and lints index.js. E.g. ESLINT_VERSION=6 npm run test will test that this configuration works with the latest version of ESLint 6.