gistfile1.js

var fsButton = document.getElementById('fsbutton'),
    container = document.getElementById('canvas');


if (window.fullScreenApi.supportsFullScreen) {
    fsButton.style.display = 'block';

    fsButton.addEventListener('click', function() {
        if (fsButton.className == 'fs-off') {
            window.fullScreenApi.requestFullScreen(container);
        } else {
            window.fullScreenApi.cancelFullScreen(container);
        }
    }, true);

    container.addEventListener(fullScreenApi.fullScreenEventName, function() {
        if (fullScreenApi.isFullScreen()) {
            container.style.width = container.style.height = '100%';
            fsButton.className = 'fs-on';
        } else {
            fsButton.className = 'fs-off';
        }
    }, true);
} else {
    // no fullscreen support - do nothing
}