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no-unsafe-enum-comparison

Disallow comparing an enum value with a non-enum value.

✅

Extending "plugin:@typescript-eslint/recommended-type-checked" in an ESLint configuration enables this rule.

💡

Some problems reported by this rule are manually fixable by editor suggestions.

💭

This rule requires type information to run.

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:

enum Vegetable {
  Asparagus = 'asparagus',
}

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:

  • 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.
  • It aligns code to the proper enum semantics of referring to them by name and treating their values as implementation details.
.eslintrc.cjs
module.exports = {
  "rules": {
    "@typescript-eslint/no-unsafe-enum-comparison": "error"
  }
};

Try this rule in the playground ↗

Examples​

enum Fruit {
  Apple,
}

declare let fruit: Fruit;

fruit === 0;
Open in Playground
enum Vegetable {
  Asparagus = 'asparagus',
}

declare let vegetable: Vegetable;

vegetable === 'asparagus';
Open in Playground

Options​

This rule is not configurable.

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.

Separately, in the rare case of relying on an third party enums that are only imported as types, it may be difficult to adhere to this rule. You might consider using ESLint disable comments for those specific situations instead of completely disabling this rule.

Type checked lint rules are more powerful than traditional lint rules, but also require configuring type checked linting. See Performance Troubleshooting if you experience performance degredations after enabling type checked rules.

Resources​