nonNullableTypeAssertions

Reports type assertions that can be replaced with non-null assertions.

✅ This rule is included in the ts stylistic and stylisticStrict presets.

When asserting a type that only removes null or undefined from a union, a non-null assertion (!) is more concise and expressive than a full type assertion (as or angle-bracket syntax).

For example, if a value is of type string | null, asserting it as string can be replaced with a non-null assertion: value!.

This rule reports type assertions where the only difference between the original and asserted type is nullability, suggesting the use of a non-null assertion instead.

Examples

❌ Incorrect

declare const value: string | null;
value as string;

declare const value: number | undefined;
<number>value;

declare const value: string | number | null;
value as string | number;

✅ Correct

declare const value: string | null;
value!;

declare const value: number | undefined;
value!;

declare const value: string | number | null;
value!;

declare const value: string | number | null;
value as string;

declare const value: any;
value as string;

Options

This rule is not configurable.

When Not To Use It

If your codebase prefers explicit type assertions for clarity or documentation, you may disable this rule. Alternatively, if you avoid non-null assertions entirely due to their potential for runtime errors, this rule may not be appropriate.

Further Reading

• TypeScript: Non-null assertion operator
• TypeScript: Type Assertions

Equivalents in Other Linters

• ESLint: @typescript-eslint/non-nullable-type-assertion-style
• Oxlint: typescript/non-nullable-type-assertion-style