  We investigate the electromagnetic form factor $F(q^2)$ of the meson by using
the solvable $\phi^{3}$ scalar field model in $(1+1)$ dimensions. As the
transverse rotations are absent in $(1+1)$ dimensions, the advantage of the
light-front dynamics (LFD) with the light-front time $x^+ = x^0 + x^3$ as the
evolution parameter is maximized in contrast to the usual instant form dynamics
(IFD) with the ordinary time $x^0$ as the evolution parameter. In LFD, the
individual $x^+$-ordered amplitudes contributing to $F(q^2)$ are invariant
under the boost, i.e., frame-independent, while the individual $x^0$-ordered
amplitudes in IFD are not invariant under the boost but dependent on the
reference frame. The LFD allows to get the analytic result for the one-loop
triangle diagram which covers not only the spacelike ($q^{2}<0$) but also
timelike region ($q^{2}>0$). Using the analytic results, we verify that the
real and imaginary parts of the form factor satisfy the dispersion relations in
the entire $q^{2}$ space. Comparing with the results in $(3+1)$ dimensions, we
discuss the transverse momentum effects on $F(q^2)$ . We also discuss the
longitudinal charge density in terms of the boost invariant variable $\tilde z
= p^+ x^-$ in LFD.
