A hinge assembly (10) for joining a cover section (012) to a body section (014) of a foldable electronic device (01) includes: a button (1); a locking element (2); a main shaft (4); a driving spring (3); a cam (5) including a latching cam surface (54) on one end thereof, and two reverse rotating grooves (56) on another end thereof; a barrel (6) including two latching posts (62) engaging in the grooves; an end shaft (8); and a torsion spring (7) including two end portions attached to the barrel and the end shaft. The button, the locking element and the driving spring are located around one end of the main shaft, and the cam and the barrel are located around another end of the main shaft. When the button is pushed, the hinge assembly fully opens the cover section from body section. This provides a user with convenient one-handed operation.