Skip to main content

no-unnecessary-type-constraint

Disallows unnecessary constraints on generic types.

Attributes​

  • Included in configs
    • ✅ Recommended
    • 🔒 Strict
  • Fixable
    • 🔧 Automated Fixer
    • 🛠 Suggestion Fixer
  • 💭 Requires type information

Rule Details​

Type parameters (<T>) may be "constrained" with an extends keyword (docs). When not provided, type parameters happen to default to:

  • As of TypeScript 3.9: unknown (docs)
  • Before that, as of 3.5: any (docs)

It is therefore redundant to extend from these types in later versions of TypeScript.

Examples of code for this rule:

interface FooAny<T extends any> {}
interface FooUnknown<T extends unknown> {}

type BarAny<T extends any> = {};
type BarUnknown<T extends unknown> = {};

class BazAny<T extends any> {
  quxUnknown<U extends unknown>() {}
}

class BazUnknown<T extends unknown> {
  quxUnknown<U extends unknown>() {}
}

const QuuxAny = <T extends any>() => {};
const QuuxUnknown = <T extends unknown>() => {};

function QuuzAny<T extends any>() {}
function QuuzUnknown<T extends unknown>() {}

Options​

// .eslintrc.json
{
  "rules": {
    "@typescript-eslint/no-unnecessary-type-constraint": "error"
  }
}

This rule is not configurable.

When Not To Use It​

If you don't care about the specific styles of your type constraints, or never use them in the first place, then you will not need this rule.