Lookup table for multiple Key Press

Question

I am trying to create a look up table ( as i have large number of keys to handle) for handling my keys functionality. So far i have been able to handle single key presses as shown below:

(function(){
       document.body.addEventListener('keydown',keysHandler,false); 
       var keyLookUp = {37:leftKey,39:rightKey,40:DownKey...etc}

       function keysHandler(e){
          event = e || window.event;
          var keycode = event.which || event.keyCode;
          keyLookUp[keycode](e);
       }

       function leftKey(e){

        }

       function rightKey(e){

       }

       function DownKey(e){

       }

})();

How can i modify the above code to handle the multiple key press functionality also?? like pressing Shift + left key

Answer 1

How can i modify the above code to handle the multiple key press [such as] pressing Shift + ←

The keys Shift, Ctrl, Alt and Alt Gr are modifier keys, this means that they're sent as part of the event you call e and are stored as e.shiftKey, e.ctrlKey, e.altKey and e.altGraphKey, respectively.

So what does this mean for you? If you want to keep your current structure, I see you as having three choices; you can

1. write completely different functions for the modified versions, e.g.

   keyLookUp['37sc'] = leftKeyShiftCtrl;
   
   keyLookUp[
       keycode
       + (e.shiftKey ? 's' : '')
       + (e.ctrlKey? 'c' : '')
       + (e.altKey ? 'a' : '')
   ](e);
   

2. look at these values in you current handlers

   // inside fn
   if (e.shiftKey) {/* different code path */}
   

3. pass these as parameters into your handlers (which take extra args)

   function leftKey(e, shift, ctrl, alt) { /* ... */ }
   
   keyLookUp[keycode](e, e.shiftKey, e.ctrlKey, e.altKey);
   

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For any combination of keys, you need to track keydown and keyup, see this question