A novel crosslinking strategy for injectable "click" hydrogels is reported. Precursors containing thiol or epoxy groups are facilely synthesized by polycondensation and radical polymerization respectively, which are used to in situ form hydrogels under physiological conditions within tens of seconds via thiol-epoxy reaction. The suitable gelation time and low cytotoxicity of this kind of hydrogels make it a potential candidate as implanted material for biomedical applications.