pure

eslint-plugin-pure is an ESLint plugin designed to help developers write purely functional JavaScript code by statically analyzing and disallowing language constructs that cause side effects. It enforces immutability and purity at the linting stage, making it easier to reason about code behavior and prevent bugs related to unintended side effects.

Key Features

• ExpressionStatement Prevention — Disallows statements whose results are unused, indicating potential side effects, while allowing binding to variables.
• AssignmentExpression Blocking — Prohibits assignment expressions to enforce immutability.
• UpdateExpression Restriction — Bans update expressions (like ++ or --) to prevent state mutation.
• SequenceExpression Disallowance — Forbids sequence expressions to ensure no expressions are evaluated solely for side effects.
• ES6 Module Requirement — Requires ES6 modules, as module.exports is considered impure.

Philosophy

The plugin promotes a purely functional programming style by statically enforcing rules that eliminate side effects, helping developers write more predictable and maintainable code, particularly in reducers or entity modules.