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.

该 issue 未提供文件路径或测试路径。首先在 TypeScript 编译器及其测试中定位 throw 语句的类型检查，然后检查 nullable 表达式和 any 表达式的处理方式。当列出的非 Error 表达式被拒绝，而 Error 表达式和 any 表达式仍被允许，且不改变生成的 JavaScript 时，即视为完成。