eslint-plugin-scats

ESLint plugin with rules for safer and more idiomatic usage of scats.

Installation

npm install --save-dev eslint eslint-plugin-scats

If you lint TypeScript, also install:

npm install --save-dev @typescript-eslint/parser

Configs

Legacy config

Recommended:

module.exports = {
  plugins: ['scats'],
  extends: ['plugin:scats/recommended'],
};

Strict:

module.exports = {
  plugins: ['scats'],
  extends: ['plugin:scats/strict'],
};

Flat config

const scats = require('eslint-plugin-scats');

module.exports = [
  {
    plugins: {
      scats,
    },
    rules: {
      ...scats.configs.recommended.rules,
    },
  },
];

For strict mode use scats.configs.strict.rules.

Rules

Recommended

• scats/to-array-terminal: requires .toArray to be terminal in scats call chains
• scats/no-array-option-fallback: disallows Option#getOrElseValue([]), Option#getOrElse(() => []), Option#getOrElseValue(Nil.toArray), and similar array fallbacks; prefer keeping values as scats collections and using Nil or an appropriate empty collection
• scats/no-collection-emptiness-comparison: prefers .isEmpty and .nonEmpty over comparing scats collection .length or .size to zero
• scats/no-collection-get-zero: disallows Collection#get(0); prefer head or headOption to make first-element access explicit
• scats/no-explicit-empty: disallows creating obviously empty scats collections via constructors/factories when Nil or *.empty should be used
• scats/no-option-nullish-fallback: disallows option(null)/option(undefined) in favor of none, disallows Option#getOrElse(() => null), Option#getOrElseValue(null), the corresponding undefined fallbacks, and redundant patterns such as option(existingOption.orNull) or option(existingOption.orNull).orElse(() => option(fallback.orNull)) when the original Option should be used directly
• scats/no-option-foreach-assignment: disallows let result = none followed by mutation inside option(...).foreach(...); prefer deriving the value with map or flatMap
• scats/prefer-get-or-else-value: prefers Option#getOrElseValue(...) over Option#getOrElse(() => ...) when the callback returns an explicit constant such as a literal or static template string, and prefers Option#orElseValue(...) over Option#orElse(() => someOption) when the fallback is already an Option
• scats/no-useless-to-array-iteration: disallows for...of (... of collection.toArray) for confirmed scats collections and auto-fixes to iterate the scats collection directly

Strict

• includes all recommended rules
• scats/no-array-construction: disallows storing JavaScript arrays in local variables or class fields; inline arrays and object property assignments for external APIs remain allowed
• scats/no-array-mutation: disallows mutating JavaScript arrays directly via mutating methods, index writes, or length = ...; this rule uses TypeScript type information to avoid false positives on non-array objects with methods like push
• scats/no-array-typed-variable: disallows local variables and class fields typed as Array<T>, ReadonlyArray<T>, or T[]; this catches cases where .toArray results are stored explicitly as JavaScript arrays. For DTOs or external contracts, annotate the class with @scatsAllowArrayTypes
• scats/no-nullish-syntax: disallows ?. and ??; prefer explicit Option flows such as option(x).flatMap(...) and option(x).getOrElseValue(...)

Development

npm test