💻

• Would you like to work on a fix?

How are you using Babel?

Programmatic API (babel.transform, babel.parse)

Input code

import parser from "@babel/parser";
const file = await parser.parse("export default class {}", {sourceType: "module"});
const exportDecl = file.program.body[0] as ExportDefaultDeclaration;
const classDecl = exportDecl.declaration as ClassDeclaration;
console.log(classDecl.id.name); // TypeError: Cannot read properties of null (reading 'name')
// TypeScript does not catch this error since the type of `id` is `Identifier` not `Identifier | null`.

Configuration file name

No response

Configuration

No response

Current and expected behavior

When a class is a default export, it is not required to have an identifier, so parse correctly outputs a ClassDeclaration with its id property set to null when the identifier is omitted. However, the ClassDeclaration type from @babel/types does not have an optional id property. This results in situations where TypeScript users will be confident that the id of a ClassDeclaration is non-null when it might not be.

The ClassDeclaration interface's id property's type should optional and its type annotation should be Identifier | null.

See https://tc39.es/ecma262/2023/multipage/ecmascript-language-functions-and-classes.html#prod-ClassDeclaration

Environment

• @babel/parser@7.22.14
• @babel/types@7.22.11

Possible solution

The ClassDeclaration interface's id property's type should optional and its type annotation should be Identifier | null.

Additional context

No response