olizilla gets up close and functional with javascript. withCanvas provides a temporary canvas to another function, and always remembers to clean up after itself.

withCanvas.js

// Provide a function with a temporary canvas, encapsulating the creation and clean up code.
function withCanvas(/*canvas => Any*/  use) {
	var b = document.body;

	// create canvas
	var canvas = document.createElement("canvas");

        // canvas doesn't draw well unless it's added to the page			
	b.appendChild(canvas);

	// do the user code
	var result = use(canvas);

	// clean up
	b.removeChild(canvas);
	
	// return anything there is to return
	return result;
}

var video = document.getElementById('someVideo');

// usage, do something with a temporary canvas
var src = withCanvas( function(canvas){     // anonymous function, canvas => String
              var ctx = canvas.getContext('2d');	
	      ctx.drawImage(video, 0, 0, canvas.width, canvas.height);
	      return ctx.canvas.toDataURL('image/png');
          });