E0239: TypeScript assignment-asserted fields are not supported in JavaScript

In TypeScript, ! after a class field name indicates a definite assignment assertion. It is a syntax error to use a definite assignment assertion on a class field in JavaScript code:

class AccountBuilder {
  name!: string;
  address = null;

  setName(value) {
    this.name = value;
    return this;
  }

  setAddress(value) {
    this.address = value;
    return this;
  }
}

To fix this error, remove the ! after the field name, and remove the field's type:

class AccountBuilder {
  name;
  address = null;

  setName(value) {
    this.name = value;
    return this;
  }

  setAddress(value) {
    this.address = value;
    return this;
  }
}

Introduced in quick-lint-js version 2.6.0.

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