Function emscripten_sys::emscripten_idb_async_exists

pub unsafe extern fn emscripten_idb_async_exists(db_name: *const c_char,
                                                 file_id: *const c_char,
                                                 arg: *mut c_void,
                                                 oncheck: em_idb_exists_func,
                                                 onerror: em_arg_callback_func)