title: how to remove event listener from fabricjs canvas
body: <p>I am using fabricjs to build an interactive  map in html5. </p>
  
  <p>When the DOM loads, I add my mouseover listener to my fabricjs canvas instance by calling: *my_event_setter( <strong>true</strong> )*.</p>
  
  <p>Then for the sake of testing, I want to remove the listener once I do my first mouseover by calling: *my_event_setter( <strong>false</strong> )*. That should thus remove the mouseover listener, but it does not.</p>
  
  <pre><code>my_event_setter = function( toggle )
    { var lvo =  { 'object:over' : function(e){ mouseover_handler( e ) } } ;
      toggle ? my_fabric_canvas.on( lvo ) : my_fabric_canvas.off( lvo ) ;
    } 
  mouseover_handler = function( e )
    { my_event_setter( false ) ;
    } 
  </code></pre>