A simple function to toggle fullscreen in JavaScript. It work well on Firefox and Webkit browsers.

toggleFullscreen.js

/**
 * Toggle fullscreen function who work with webkit and firefox.
 * @function toggleFullscreen
 * @param {Object} event
 */
function toggleFullscreen(event) {
  var element = document.body;

	if (event instanceof HTMLElement) {
		element = event;
	}

	var isFullscreen = document.webkitIsFullScreen || document.mozFullScreen || false;

	element.requestFullScreen = element.requestFullScreen || element.webkitRequestFullScreen || element.mozRequestFullScreen || function () { return false; };
	document.cancelFullScreen = document.cancelFullScreen || document.webkitCancelFullScreen || document.mozCancelFullScreen || function () { return false; };

	isFullscreen ? document.cancelFullScreen() : element.requestFullScreen();
}

Brilliant.

simply incredible!

Great work! Here's a version that uses ES6 features for more streamlined code:

function toggleFullscreen(view = document.body) {
    view.requestFullScreen = view.requestFullScreen || view.webkitRequestFullScreen || view.mozRequestFullScreen || function () { return false };
    document.cancelFullScreen = document.cancelFullScreen || document.webkitCancelFullScreen || document.mozCancelFullScreen || function () { return false };
    (document.webkitIsFullScreen || document.mozFullScreen || false) ? document.cancelFullScreen() : view.requestFullScreen();
}

We can trust the person calling the function to either pass in no view element and wants the body to go fullscreen, or they'll pass in an appropriate HTMLElement.