  The $J/{\psi}$ weak decays are rare but possible within the standard model of
elementary particles. Inspired by the potential prospects at the future
intensity frontier, the $C$ parity violating $J/{\psi}$ ${\to}$
${\pi}{\eta}^{({\prime})}$, ${\eta}{\eta}^{\prime}$ decays and the strangeness
changing $J/{\psi}$ ${\to}$ ${\pi}K$, $K{\eta}^{({\prime})}$ decays are studied
with the perturbative QCD approach. It is found that the $J/{\psi}$ ${\to}$
${\eta}{\eta}^{\prime}$ decays have relatively large branching ratios, about
the order of $10^{-11}$, which might be within the measurement capability and
sensitivity of the future STCF experiment.
