  We study the newly observed charmoniumlike state $Z_{cs}(3985)$ in the
framework of chiral effective field theory. The interaction kernel of the
$\bar{D}_sD^\ast/\bar{D}^\ast_sD$ system is calculated up to the
next-to-leading order with the explicit chiral dynamics. With the fitted
parameters extracted from the $Z_c(3900)$ data as inputs, the mass, width and
event distributions of the $Z_{cs}(3985)$ are very consistent with the
experimental measurements. Our studies strongly support the $Z_{cs}(3985)$ as
the partner of the $Z_c(3900)$ in the SU(3)$_f$ symmetry and the
$\bar{D}_sD^\ast/\bar{D}^\ast_sD$ molecular resonance with the same dynamical
origin as the other charged heavy quarkoniumlike states. We precisely predict
the resonance parameters of the unobserved states in $\bar{D}_s^\ast D^\ast$,
$B^\ast_s \bar{B}/B_s\bar{B}^\ast$ and $B_s^\ast\bar{B}^\ast$ systems, and
establish a complete spectrum of the charged charmoniumlike and bottomoniumlike
states with the $I(J^P)$ quantum numbers $1(1^+)$ and $\frac{1}{2}(1^+)$,
respectively.
