  We study the purely leptonic decays of heavy-flavored charged pseudoscalar
(P) and vector (V) mesons ($D_{(s)}^{(*)+}$, $B_{(c)}^{(*)+}$) in the
relativistic independent quark (RIQ) model based on an average
flavor-independent confining potential in equally mixed scalar-vector harmonic
form. We first compute the mass spectra of the ground-state-mesons and fix the
model parameters necessary for the present analysis. Using the meson wave
functions derivable in the RIQ model, and model parameters so fixed from hadron
spectroscopy, we predict the decay constants: $f_{P(V)}$, ratios of decay
constants: $f_{V}/f_{P}$, $f_{P_1}/f_{P_2}$, $f_{V_1}/f_{V_2}$, and the
branching fractions (BFs): ${\cal B}(P(V)\to l^+\nu_l)$, $l=e, \mu, \tau$,
which agree with the available experimental data and other Standard Model (SM)
predictions. For the unmeasured decay constants especially in the purely
leptonic decays of the charged vector mesons, our predictions could be tested
in the upcoming Belle-II, SCTF, CEPC, FCC-ee and LHCb experiments in near
future.
