okta-oidc-js is a monorepo, containing multiple packages/libraries. We’re working to break these packages out of the mono repo because its a little confusing/messy having it set up this way. Suffice to say, it is not really a separate JS library unto itself.
For your SPA, you will want to use either okta-auth-js, or, if you are using the associated framework, okta-angular, okta-react, or okta-vue