no-unnecessary-type-assertion

Disallow type assertions that do not change the type of an expression.

This rule prohibits using a type assertion that does not change the type of an expression.

Attributes

This rule aims to prevent unnecessary type assertions.

Examples of code for this rule:

const foo = 3;
const bar = foo!;

const foo = <3>3;

type Foo = 3;
const foo = <Foo>3;

type Foo = 3;
const foo = 3 as Foo;

function foo(x: number): number {
  return x!; // unnecessary non-null
}

const foo = <number>3;

const foo = 3 as number;

const foo = 'foo' as const;

function foo(x: number | undefined): number {
  return x!;
}

.eslintrc.cjs
module.exports = {
  "rules": {
    "@typescript-eslint/no-unnecessary-type-assertion": "error"
  }
};

This rule accepts an options object with the following properties:

interface Options {
  /**
   * A list of type names to ignore.
   */
  typesToIgnore?: string[];
}

const defaultOptions: Options = [{}];

With @typescript-eslint/no-unnecessary-type-assertion: ["error", { typesToIgnore: ['Foo'] }], the following is correct code":

type Foo = 3;
const foo: Foo = 3;

If you don't care about having no-op type assertions in your code, then you can turn off this rule.