diff --git a/packages/eslint-plugin/docs/rules/no-unsafe-enum-comparison.mdx b/packages/eslint-plugin/docs/rules/no-unsafe-enum-comparison.mdx index 7988317b5b6d..4b25e785e87d 100644 --- a/packages/eslint-plugin/docs/rules/no-unsafe-enum-comparison.mdx +++ b/packages/eslint-plugin/docs/rules/no-unsafe-enum-comparison.mdx @@ -9,7 +9,9 @@ import TabItem from '@theme/TabItem'; > > See **https://typescript-eslint.io/rules/no-unsafe-enum-comparison** for documentation. -The TypeScript compiler can be surprisingly lenient when working with enums. String enums are widely considered to be safer than number enums, but even string enums have some pitfalls. For example, it is allowed to compare enum values against literals: +The TypeScript compiler can be surprisingly lenient when working with enums. +While overt safety problems with enums were [resolved in TypeScript 5.0](https://devblogs.microsoft.com/typescript/announcing-typescript-5-0/#all-enums-are-union-enums), some logical pitfalls remain permitted. +For example, it is allowed to compare enum values against non-enum values: ```ts enum Vegetable { @@ -21,7 +23,9 @@ declare const vegetable: Vegetable; vegetable === 'asparagus'; // No error ``` -The above code snippet should instead be written as `vegetable === Vegetable.Asparagus`. Allowing literals in comparisons subverts the point of using enums in the first place. By enforcing comparisons with properly typed enums: +The above code snippet should instead be written as `vegetable === Vegetable.Asparagus`. +Allowing non-enums in comparisons subverts the point of using enums in the first place. +By enforcing comparisons with properly typed enums: - It makes a codebase more resilient to enum members changing values. - It allows for code IDEs to use the "Rename Symbol" feature to quickly rename an enum. @@ -39,17 +43,22 @@ enum Fruit { declare let fruit: Fruit; +// bad - comparison between enum and explicit value instead of named enum member fruit === 0; -``` -```ts enum Vegetable { Asparagus = 'asparagus', } declare let vegetable: Vegetable; +// bad - comparison between enum and explicit value instead of named enum member vegetable === 'asparagus'; + +declare let anyString: string; + +// bad - comparison between enum and non-enum value +anyString === Vegetable.Asparagus; ``` @@ -63,9 +72,7 @@ enum Fruit { declare let fruit: Fruit; fruit === Fruit.Apple; -``` -```ts enum Vegetable { Asparagus = 'asparagus', } @@ -80,7 +87,12 @@ vegetable === Vegetable.Asparagus; ## When Not To Use It -If you don't mind number and/or literal string constants being compared against enums, you likely don't need this rule. +If you don't mind enums being treated as a namespaced bag of values, rather than opaque identifiers, you likely don't need this rule. + +Sometimes, you may want to ingest a value from an API or user input, then use it as an enum throughout your application. +While validating the input, it may be appropriate to disable the rule. +Alternately, you might consider making use of a validation library like [Zod](https://zod.dev/?id=native-enums). +See further discussion of this topic in [#8557](https://github.com/typescript-eslint/typescript-eslint/issues/8557). -Separately, in the rare case of relying on an third party enums that are only imported as `type`s, it may be difficult to adhere to this rule. +Finally, in the rare case of relying on an third party enums that are only imported as `type`s, it may be difficult to adhere to this rule. You might consider using [ESLint disable comments](https://eslint.org/docs/latest/use/configure/rules#using-configuration-comments-1) for those specific situations instead of completely disabling this rule. diff --git a/packages/eslint-plugin/tests/docs-eslint-output-snapshots/no-unsafe-enum-comparison.shot b/packages/eslint-plugin/tests/docs-eslint-output-snapshots/no-unsafe-enum-comparison.shot index 2d883379f083..3b26a4df1d59 100644 --- a/packages/eslint-plugin/tests/docs-eslint-output-snapshots/no-unsafe-enum-comparison.shot +++ b/packages/eslint-plugin/tests/docs-eslint-output-snapshots/no-unsafe-enum-comparison.shot @@ -9,13 +9,9 @@ enum Fruit { declare let fruit: Fruit; +// bad - comparison between enum and explicit value instead of named enum member fruit === 0; ~~~~~~~~~~~ The two values in this comparison do not have a shared enum type. -" -`; - -exports[`Validating rule docs no-unsafe-enum-comparison.mdx code examples ESLint output 2`] = ` -"Incorrect enum Vegetable { Asparagus = 'asparagus', @@ -23,12 +19,19 @@ enum Vegetable { declare let vegetable: Vegetable; +// bad - comparison between enum and explicit value instead of named enum member vegetable === 'asparagus'; ~~~~~~~~~~~~~~~~~~~~~~~~~ The two values in this comparison do not have a shared enum type. + +declare let anyString: string; + +// bad - comparison between enum and non-enum value +anyString === Vegetable.Asparagus; +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ The two values in this comparison do not have a shared enum type. " `; -exports[`Validating rule docs no-unsafe-enum-comparison.mdx code examples ESLint output 3`] = ` +exports[`Validating rule docs no-unsafe-enum-comparison.mdx code examples ESLint output 2`] = ` "Correct enum Fruit { @@ -38,11 +41,6 @@ enum Fruit { declare let fruit: Fruit; fruit === Fruit.Apple; -" -`; - -exports[`Validating rule docs no-unsafe-enum-comparison.mdx code examples ESLint output 4`] = ` -"Correct enum Vegetable { Asparagus = 'asparagus', pFad - Phonifier reborn

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