How to destroy object?

Hi there,

This tracking is totally awesome and I like it.
I have made some initialization just like the example, as follow:

`var tracker = new tracking.ObjectTracker('face');
tracker.setInitialScale(4);
tracker.setStepSize(2);
tracker.setEdgesDensity(0.1);

tracking.track('#video', tracker, { camera: true });

tracker.on('track', function(event) {
context.clearRect(0, 0, canvas.width, canvas.height);

event.data.forEach(function(rect) {
context.strokeStyle = '#a64ceb';
context.strokeRect(rect.x, rect.y, rect.width, rect.height);
context.font = '11px Helvetica';
context.fillStyle = "#fff";
context.fillText('x: ' + rect.x + 'px', rect.x + rect.width + 5, rect.y + 11);
context.fillText('y: ' + rect.y + 'px', rect.x + rect.width + 5, rect.y + 22);
});
});`

But I do not know how to destroy the object so the web app will free some memory used.

Thank you so much.