  For the case of quantum loop algebras $\mathrm U_q(\mathcal
L(\mathfrak{sl}_{l + 1}))$ with $l = 1, 2$ we find the $\ell$-weights and the
corresponding $\ell$-weight vectors for the representations obtained via
Jimbo's homomorphism, known also as evaluation representations. Then we find
the $\ell$-weights and the $\ell$-weight vectors for the $q$-oscillator
representations of Borel subalgebras of the same quantum loop algebras. This
allows, in particular, to relate $q$-oscillator and prefundamental
representations.
