html5 canvas ping pong game bug

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Javascript

Hello everyone , I am a newbie to Javascript and lack strong knowledge of basics of this language, yet I tried to make a simple ping-pong game to which i was almost successful.

Except one error that during playing the game sometimes when we press the space key the ball starts moving quite fastly (keep on pressing space key during playing), dont know what is the reason and know there will be quite bugs in program,so plz dont shout at me. :P

Help me there and tell me how can i improve it. Plz reply soon.

Here is the fiddle for it :-
http://jsfiddle.net/gurjitmehta/vc2u0zrt/

experimental view of debugging in mobile :-
http://jsfiddle.net/m/rwc/