Disallows generator functions that have no `yield`. JavaScript provides generator functions expressed as `function*`, where we can pause and later resume the function execution at the middle points. At these points we use the `yield` keyword. In other words, it makes no sense at all to create generator functions that contain no `yield` keyword, since such functions could be written as normal functions. ### Invalid: ```typescript function* f1() { return "f1"; } ``` ### Valid: ```typescript function* f1() { yield "f1"; } // generator function with empty body is allowed function* f2() {} function f3() { return "f3"; } ```