E0301: 'this' parameters are not allowed in arrow functions

TypeScript allows you to add a type annotation to the implicit this parameter explicitly. This is possible in methods, in functions declared with the function keyword, and in function types. It is a syntax error to write a this parameter explicitly in an arrow function:

// Example from TypeScript documentation. SPDX license: MIT
// Copyright (c) Microsoft Corporation
interface DB {
  filterUsers(filter: (this: User) => boolean): User[];
}
let admins = db.filterUsers((this: User) => {
  return this.admin;
});

To fix this error, write a function with the function keyword instead of an arrow function:

let admins = db.filterUsers(function (this: User) {
  return this.admin;
});

Introduced in quick-lint-js version 2.10.0.

Documentation for other errors