Detail Notes :
1. if the KeyboardEvent doesn't have a 'key' option,
2. in the keyDown event,
3. in the keyboard input is in the range 0-9,
4. returns the number corresponding to event.key
Detail Notes :
1. if the browser version is 'Chrome/38.0.2125.0',
2. in the keyUp event,
3. in the event capture step,
4. change the 'repeat' option of KeyboardEvent to false
