A charger for wirelessly charging an electronic device by electromagnetic induction includes a coil assembly and a control unit. The control unit includes an identification module, a detection module, a comparing module, and an allocating module. The identification module identifies the electronic device. The detection module detects power rating and required electric power of the electronic device. The comparing module compares residual electric power of the wireless charger with the required electric power of the electronic device. The allocating module selects a portion of the residual electric power of the wireless charger. The coil assembly converts the portion of the residual electric power of the wireless charger into electromagnetic waves, and directs the electromagnetic waves to the electronic device.