A bumper includes a supporting member, a base, a flange, a connecting arm, and a resetting assembly. The base is fixedly connected to the supporting member. The connecting arm has a rotating portion rotatably positioned between the flange and the supporting member. The resetting assembly includes a resisting member and an elastic member. The resisting member is slidably connected to the supporting member. The elastic member is configured for producing an elastic force to drive the resisting member to resist the rotating portion of the connecting arm. One of the rotating portion and the resisting member defines a receiving groove, and the other one of the rotating portion and the resisting member defines a restricting protrusion rotatably engaging in the receiving groove.