identify an object on canvas by a click event

into this simple code I use an eventListener which doesnt look to work at all. The canvas display an image and the given hitpaint function is supposed determines whether a click occurs. I cant understand why the eventListener behaves like that. Any insight would be helpful.

mycanv.addEventListener("click", function(e){                                                                                                                                                                                           
  var output = document.getElementByID("output");                                                                                                                                                                                         
  ctx.fillStyle = 'blue';                                                                                                                                                                                                                 
  //ctx.clearRect(0,0,100,20);                                                                                                                                                                                                            
    if (hitpaint){                                                                                                                                                                                                                        
  //ctx.fillText("hit",100,20);                                                                                                                                                                                                           
  output.innerHTML = "hit";                                                                                                                                                                                                               
    }                                                                                                                                                                                                                                     
    else                                                                                                                                                                                                                                  
  //ctx.fillText("miss",100,20);                                                                                                                                                                                                          
  output.innerHTML = "miss";                                                                                                                                                                                                              

  }, false);                                                                                                                                                                                                                                                                                                                            

the hitpaint looks like that:

function hitpaint(mouse_event) {                                                                                                                                                                                                        

  var bounding_box=mycanv.getBoundingClientRect();                                                                                                                                                                                        


  var mousex=(mouse_event.clientX-bounding_box.left) *                                                                                                                                                                                    
  (mycanv.width/bounding_box.width);                                                                                                                                                                                                      
  var mousey=(mouse_event.clientY-bounding_box.top) *                                                                                                                                                                                     
  (mycanv.height/bounding_box.height);                                                                                                                                                                                                    
  var pixels=ctx.getImageData(mousex,mousey,1,1);                                                                                                                                                                                         

  for (var i=3; i<pixels.data.length; i+=4) {                                                                                                                                                                                             
    // If we find a non-zero alpha we can just stop and return                                                                                                                                                                            
    // "true" - the click was on a part of the canvas that's                                                                                                                                                                              
    // got colour on it.                                                                                                                                                                                                                  
    if ( pixels.data[i]!==0 ) return true;                                                                                                                                                                                                
    }                                                                                                                                                                                                                                     


    // The function will only get here if none of the pixels matched in                                                                                                                                                                   

    return false;                                                                                                                                                                                                                         
    }

Finally the main loop which display the picture in random location into the canvas:

function start(){                                                                                                                                                                                                                       

    // main game function, called on page load                                                                                                                                                                                            
    setInterval( function() {                                                                                                                                                                                                             

      ctx.clearRect(cat_x, cat_y, 100, 100);                                                                                                                                                                                              
      cat_x = Math.random() * mycanv.width-20;                                                                                                                                                                                            
      cat_y = Math.random() * mycanv.height-20;                                                                                                                                                                                           
     draw_katy(cat_x,cat_y);                                                                                                                                                                                                              

      }, 1000);                                                                                                                                                                                                                           
  }