Disallowing `throw`ing expressions that aren't assignable to `Error`

Search Terms

throw, throwing non-error

Suggestion

Add typechecking to throw statement, allowing it to only throw Errors and anys.

Code currently allowed, but with strong potential for bugs:

throw null;
throw undefined;
throw 'foobar';
throw ''; 
throw 42;
throw {foo: 'bar'};
throw potentiallyNullable; // with –strictNullChecks

After implementing this feature request, such code wouldn't be allowed.

Use Cases

Even if it's possible to throw non-errors in JavaScript code, it's extremely confusing and hard to debug. Failing to properly handle such cases happened even to Mozilla.

Examples

Forbidden code:

throw null;
throw undefined;
throw 'foobar';
throw 42;
throw {foo: 'bar'};
throw potentiallyNullable; // with –strictNullChecks

Allowed:

throw new Error();
throw null as any;

Checklist

My suggestion meets these guidelines:

• This wouldn't be a breaking change in existing TypeScript/JavaScript code - it can break existing TypeScript code.
• This wouldn't change the runtime behavior of existing JavaScript code
• This could be implemented without emitting different JS based on the types of the expressions
• This isn't a runtime feature (e.g. library functionality, non-ECMAScript syntax with JavaScript output, etc.)
• This feature would agree with the rest of TypeScript's Design Goals.

この issue にはファイルパスもテストパスもありません。まず TypeScript コンパイラーとそのテストで throw ステートメントの型チェックを探し、次に nullable 式と any 式がどのように扱われているかを確認してください。指定された非 Error 式が拒否され、Error 式と any 式は引き続き許可され、出力される JavaScript が変更されなければ完了です。