throttle back canvas drawing on drag / mousemove events

gistfile1.js

var last_draw;

function draw(e) {
  var this_draw = +(new Date());
  if(!last_draw || this_draw - last_draw > 20) {
    last_draw = this_draw;
    // window.reqAnimFrame is defined elsewhere to provide cross-browser
    // requestAnimationFrame support with setTimeout fallback 
    window.reqAnimFrame(function() {
      // draw logic
    });
  }
}

// binding (using jquery)
// in this case the canvas is the size of the entire window
// and animation is intended to fire / update 
// while dragging an element anywhere over the whole thing

$(window).bind("dragover", draw);