For $x \in \mathbb{R} - \{0,1\}$, let $f_1(x)=\dfrac{1}{x}$, $f_2(x)=1-x$, and $f_3(x)=\dfrac{1}{1-x}$ be three given functions. If a function $J(x)$ satisfies $(f_2 \circ J \circ f_1)(x)=f_3(x)$, then $J(x)$ is equal to: