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See our getting started guide.

The following rulesets are made available by this plugin.

Presets:

• Strict (configs.strict)
  Enforce recommended rules designed to strictly enforce functional programming.

• Recommended (configs.recommended)
  Has the same goal as thestrict preset but a little more lenient, allowing for functional-like coding styles andnicer integration with non-functional 3rd-party libraries.

• Lite (configs.lite)
  Good if you're new to functional programming or are converting a large codebase.

Categorized:

• Currying (configs.currying)
  JavaScript functions support syntax that is not compatible with curried functions. To enforce currying, this syntaxshould be prevented.

• No Exceptions (configs.noExceptions)
  Functional programming style does not use run-time exceptions. Instead expressions produces values to indicate errors.

• No Mutations (configs.noMutations)
  Prevent mutating any data as that's not functional

• No Other Paradigms (configs.noOtherParadigms)
  JavaScript is multi-paradigm, allowing not only functional, but object-oriented as well as other programming styles.To promote a functional style, prevent the use of other paradigm styles.

• No Statements (configs.noStatements)
  In functional programming everything is an expression that produces a value.JavaScript has a lot of syntax that is just statements that does not produce a value.That syntax has to be prevented to promote a functional style.

• Stylistic (configs.stylistic)
  Enforce code styles that can be considered to be more functional.

Other:

• All (configs.all)
  Enables all rules defined in this plugin.

• Off (configs.off)
  Disable all rules defined in this plugin.

• Disable Type Checked (configs.disableTypeChecked)
  Disable all rules that require type information.

• External Vanilla Recommended (configs.externalVanillaRecommended)
  Configures recommendedvanilla ESLint rules.

• External TypeScript Recommended (configs.externalTypeScriptRecommended)
  Configures recommendedTypeScript ESLint rules.Enabling this ruleset will also enable the vanilla one.

Thebelow section gives details on which rules are enabled by each ruleset.

💼 Configurations enabled in.
⚠️ Configurations set to warn in.
🚫 Configurations disabled in.
☑️ Set in thelite configuration.
✅ Set in therecommended configuration.
🔒 Set in thestrict configuration.
🎨 Set in thestylistic configuration.
🔧 Automatically fixable by the--fix CLI option.
💡 Manually fixable byeditor suggestions.
💭 Requirestype information.
❌ Deprecated.

Name	Description	💼	⚠️	🚫	🔧	💡	💭	❌
functional-parameters	Enforce functional parameters.	☑️ ✅ 🔒					💭

Name	Description	💼	⚠️	🚫	🔧	💡	💭	❌
no-promise-reject	Disallow rejecting promises.
no-throw-statements	Disallow throwing exceptions.	☑️ ✅ 🔒					💭
no-try-statements	Disallow try-catch[-finally] and try-finally patterns.	🔒		☑️ ✅

Name	Description	💼	⚠️	🚫	🔧	💡	💭	❌
immutable-data	Enforce treating data as immutable.	☑️ ✅ 🔒					💭
no-let	Disallow mutable variables.	☑️ ✅ 🔒
prefer-immutable-types	Require function parameters to be typed as certain immutability	☑️ ✅ 🔒			🔧	💡	💭
prefer-readonly-type	Prefer readonly types over mutable types.				🔧		💭	❌
type-declaration-immutability	Enforce the immutability of types based on patterns.	☑️ ✅ 🔒			🔧	💡	💭

Name	Description	💼	⚠️	🚫	🔧	💡	💭	❌
no-class-inheritance	Disallow inheritance in classes.	☑️ ✅ 🔒
no-classes	Disallow classes.	✅ 🔒		☑️
no-mixed-types	Restrict types so that only members of the same kind are allowed in them.	☑️ ✅ 🔒					💭
no-this-expressions	Disallow this access.	🔒		☑️ ✅

Name	Description	💼	⚠️	🚫	🔧	💡	💭	❌
no-conditional-statements	Disallow conditional statements.	✅ 🔒		☑️			💭
no-expression-statements	Disallow expression statements.	✅ 🔒		☑️			💭
no-loop-statements	Disallow imperative loops.	☑️ ✅ 🔒
no-return-void	Disallow functions that don't return anything.	☑️ ✅ 🔒					💭

Name	Description	💼	⚠️	🚫	🔧	💡	💭	❌
prefer-property-signatures	Prefer property signatures over method signatures.	🎨					💭
prefer-tacit	Replacesx => f(x) with justf.		🎨			💡	💭
readonly-type	Require consistently using eitherreadonly keywords orReadonly<T>	🎨			🔧		💭

In addition to the above rules, there are a few other rules we recommended.

These rules are what are included in theexternal recommended rulesets.

• no-var
  Without this rule, it is still possible to create mutablevar variables.

• no-param-reassign
  Don't allow function parameters to be reassigned, they should be treated as constants.

• prefer-const
  This rule provides a helpful fixer when converting from an imperative code style to a functional one.

• @typescript-eslint/prefer-readonly
  This rule is helpful when working with classes.

• @typescript-eslint/switch-exhaustiveness-check
  Although ourno-conditional-statements rule also performs this check,this rule has a fixer that will implement the unimplemented cases which can be useful.

See our contributing guide.

This project started as a port oftslint-immutablewhich was originally inspired byeslint-plugin-immutable.