Light-front dynamic analysis of the longitudinal charge density using the solvable scalar field model in ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mn>1</mml:mn><mml:mo>+</mml:mo><mml:mn>1</mml:mn></mml:mrow></mml:math> ) dimensions

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