eslint-plugin-no-type-assertion

Disallow type assertions in TypeScript code. The rule will forbid both as operator and the angle-bracketed syntax, unless used for const assertions or with the unknown type. The rule also forbids non-null assertions.

The following code becomes invalid:

const foo: unknown = 42;

const notAString = <string>foo; // can't perform angle-bracketed type assertion
const alsoNotAString = foo as string; // can't use `as` operator for type assertion

const objectWithOptionalProperty: { a?: number } = {};

const notANumber = objectWithOptionalProperty.a! / 2; // can't use non-null assertion operator

Installation

Ensure you have ESLint and @typescript-eslint/parser installed:

$ yarn add eslint @typescript-eslint/parser -D

Next, install this plugin:

$ yarn add eslint-plugin-no-type-assertion -D

Configuration

In your ESLint configuration, ensure you're using @typescript-eslint/parser as a parser and it's set up correctly:

{
  "parser": "@typescript-eslint/parser",
  "parserOptions": {
    "ecmaVersion": 2018
  }
}

Add eslint-plugin-no-type-assertion to the plugin list:

{
  "plugins": ["no-type-assertion"]
}

Enable the rule:

{
  "rules": {
    "no-type-assertion/no-type-assertion": "error"
  }
}