# E0228: TypeScript optional properties are not allowed in JavaScript code

`?` on class properties is a TypeScript feature. It is a syntax error to write `?` on a property in JavaScript code:

    class Entity {
      parent? = null;
    }

To fix this error, erase the `?`:

    class Entity {
      parent = null;
    }

Alternatively, rename your file to have a `.ts` or `.tsx` suffix

Introduced in quick-lint-js version 2.6.0.

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