In this paper, we explore the possibility of designing a continuous controller for a class of nonaffine system to achieve asymptotically tracking results with robustness to system uncertainties, unvanishing disturbances, and unknown control effectiveness. A robust integral of the sign of the error design is formulated to search a robust control for the nonaffine dynamics, while a time-varying gain of Nussbaum-type-function (NTF) is augmented to estimate the unknown direction and magnitude for control effectiveness. A second-order filter is employed to proceed the design when the NTF gain is involved without using any unmeasurable signals. Rigorous analysis shows that the proposed controller can asymptotically stabilizes the closed-loop system and the output tracking error. Simulation results on a Duffing-Holmes chaotic system demonstrate the effectiveness of the proposed approach.