typescript/consistent-type-assertions Style
What it does
Enforce consistent usage of TypeScript type assertions.
Why is this bad?
Mixing assertion styles (as vs angle-bracket) makes code harder to read and maintain. In some codebases, type assertions are banned in favor of safer alternatives like type annotations or satisfies.
Examples
Examples of incorrect code for this rule (default: assertionStyle: "as"):
const value = <Foo>bar;Examples of correct code for this rule (default: assertionStyle: "as"):
const value = bar as Foo;When objectLiteralTypeAssertions or arrayLiteralTypeAssertions are set to never, then the preferred syntax for type assertions on object and array literals is to use a type annotation or the satisfies operator instead of a type assertion.
Examples of incorrect code when objectLiteralTypeAssertions: "never" and arrayLiteralTypeAssertions: "never":
const obj = { a: 1 } as Foo;
const arr = [1, 2] as Foo[];Examples of correct code when objectLiteralTypeAssertions: "never" and arrayLiteralTypeAssertions: "never":
const obj: Foo = { a: 1 };
const obj = { a: 1 } satisfies Foo;Configuration
This rule accepts a configuration object with the following properties:
arrayLiteralTypeAssertions
type: "allow" | "allow-as-parameter" | "never"
Whether array literal type assertions are allowed, allowed only as parameters, or disallowed.
"allow"
Allow type assertions on array literals.
Examples of correct code with this option:
const x = [1, 2] as number[];
const x = ["a"] as Array<string>;"allow-as-parameter"
Allow type assertions on array literals only when used as a function parameter, throw target, or default value.
Examples of incorrect code with this option:
const x = [1, 2] as Foo;
const foo = () => [5] as Foo;Examples of correct code with this option:
print([5] as Foo);
throw [1, 2] as Bar;
function f(x = [5] as Foo.Bar) {}"never"
Disallow type assertions on array literals entirely.
Examples of incorrect code with this option:
const x = [1, 2] as Foo;
print([5] as Foo);Examples of correct code with this option:
const x: Foo = [1, 2];
const x = [1, 2] satisfies Foo;assertionStyle
type: "as" | "angle-bracket" | "never"
Which assertion syntax is enforced.
"as"
Enforce as syntax for type assertions.
Examples of incorrect code with this option:
const value = <Foo>bar;Examples of correct code with this option:
const value = bar as Foo;"angle-bracket"
Enforce angle-bracket syntax for type assertions.
Examples of incorrect code with this option:
const value = bar as Foo;Examples of correct code with this option:
const value = <Foo>bar;"never"
Disallow type assertions entirely.
Examples of incorrect code with this option:
const value = bar as Foo;
const value = <Foo>bar;Examples of correct code with this option:
const value: Foo = bar;
const value = bar satisfies Foo;objectLiteralTypeAssertions
type: "allow" | "allow-as-parameter" | "never"
Whether object literal type assertions are allowed, allowed only as parameters, or disallowed.
"allow"
Allow type assertions on object literals.
Examples of correct code with this option:
const x = { a: 1 } as Foo;
const x = {} as Foo<int>;"allow-as-parameter"
Allow type assertions on object literals only when used as a function parameter, throw target, or default value.
Examples of incorrect code with this option:
const x = { a: 1 } as Foo;
const x = {} as Foo<int>;Examples of correct code with this option:
print({ a: 1 } as Foo);
throw { bar: 5 } as Foo;
function f(x = {} as Foo) {}"never"
Disallow type assertions on object literals entirely.
Examples of incorrect code with this option:
const x = { a: 1 } as Foo;
print({ a: 1 } as Foo);Examples of correct code with this option:
const x: Foo = { a: 1 };
const x = { a: 1 } satisfies Foo;How to use
To enable this rule using the config file or in the CLI, you can use:
{
"rules": {
"typescript/consistent-type-assertions": "error"
}
}import { defineConfig } from "oxlint";
export default defineConfig({
rules: {
"typescript/consistent-type-assertions": "error",
},
});oxlint --deny typescript/consistent-type-assertionsVersion
This rule was added in v1.44.0.