How to pass a parameter in Koa middleware?

Question

So I have this function in Koa, that basically checks if a user can access a specific route.

exports.requireRole = async role =>
  async (ctx, next) => {
    const { user } = ctx.state.user;
    try {
      const foundUser = await User.findById(user.id);
      // If the user couldn't be found, return an error
      if (!foundUser) {
        ctx.status = 404;
        ctx.body = { errors: [{ error: ERRORS.USER_NOT_FOUND }] };
      } else {
        // Otherwise, continue checking role
        if (getRole(user.role) >= getRole(role)) {
          await next();
        }

        ctx.status = 403;
        ctx.body = { errors: [{ error: ERRORS.NO_PERMISSION }] };
      }
    } catch (err) {
      ctx.throw(500, err);
    }
  };

And I want to use it as a middleware:

router.delete('/:id', combine([jwtAuth, requireRole(ROLES.ADMIN)]), deleteUser);

But then I get an error saying:

middleware must be a function not object

This happens only when I try to pass an argument into it.

What am I doing wrong here?

Sizix Sizix · Accepted Answer · 2019-01-22T18:44:39

The issue you are having is due to the fact that Promises are objects, and async functions return Promises. You need to change your initial function to be as follows:

exports.requireRole = role =>

instead of

exports.requireRole = async role =>

I was going over middleware myself, and ran into this issue as well.

How to pass a parameter in Koa middleware?

2 Answers