best practise koa routing responses for ok and not ok - response

Question

I'm using koa-router to define an REST api.
I have a route to allow clients to patch data, for this I expect to only response with :-
OK - data patched without error
or
NOT OK - error occurred.
router.patch('/api/data', function *(next) {
if (_.has(this.query, 'id')) {
// do data patch
this.status = 200;
this.body = yield {status: 200, body: 'OK'};
} else {
this.status = 304;
this.body = yield {status: 304, body: 'expecting id};
}
});
Is there a more standard way than the above?

Answer 1

Don't yield a simple object. Only yield an object when one or more of its properties is being assigned via a yieldable (promise, thunk, generator...).
Consider returning the updated item to prevent the need for additional api calls.
this.throw() is what I use.
router.patch('/api/data', function *(next) {
if (_.has(this.query, 'id')) {
this.status = 200;
// don't yield...
this.body = {status: 200, body: 'OK'};
// consider returning the updated item to prevent the need to additional
// api calls
this.body = yield model.update(this.query.id, ...)
} else {
this.throw(304, 'expecting id', {custom: 'properties here'});
}
});

Answer 2

To mildly improve upon #James Moore's answer, you can also use this.assert(expression, [status], [message]) to short-circuit a route early if expression is not truthy.
I've converted their code to demonstrate:
router.patch('/api/data', function*(next) {
this.assert(_.has(this.query, 'id'), 304, JSON.stringify({ status: 304, body: 'expecting id' })));
this.body = JSON.stringify({ status: 200, body: 'OK' });
});