text: class VRButton {
  
  	static createButton( renderer, options ) {
  
  		if ( options ) {
  
  			console.error( 'THREE.VRButton: The "options" parameter has been removed. Please set the reference space type via renderer.xr.setReferenceSpaceType() instead.' );
  
  		}
  
  		const button = document.createElement( 'button' );
  
  		function showEnterVR( /*device*/ ) {
  
  			let currentSession = null;
  
  			async function onSessionStarted( session ) {
  
  				session.addEventListener( 'end', onSessionEnded );
  
  				await renderer.xr.setSession( session );
  				button.textContent = 'EXIT VR';
  
  				currentSession = session;
  
  			}
  
  			function onSessionEnded( /*event*/ ) {
  
  				currentSession.removeEventListener( 'end', onSessionEnded );
  
  				button.textContent = 'ENTER VR';
  
  				currentSession = null;
  
  			}
  
  			//
  
  			button.style.display = '';
  
  			button.style.cursor = 'pointer';
  			button.style.left = 'calc(50% - 50px)';
  			button.style.width = '100px';
  
  			button.textContent = 'ENTER VR';
  
  			button.onmouseenter = function () {
  
  				button.style.opacity = '1.0';
  
  			};
  
  			button.onmouseleave = function () {
  
  				button.style.opacity = '0.5';
  
  			};
  
  			button.onclick = function () {
  
  				if ( currentSession === null ) {
  
  					// WebXR's requestReferenceSpace only works if the corresponding feature
  					// was requested at session creation time. For simplicity, just ask for
  					// the interesting ones as optional features, but be aware that the
  					// requestReferenceSpace call will fail if it turns out to be unavailable.
  					// ('local' is always available for immersive sessions and doesn't need to
  					// be requested separately.)
  
  					const sessionInit = { optionalFeatures: [ 'local-floor', 'bounded-floor', 'hand-tracking', 'layers' ] };
  					navigator.xr.requestSession( 'immersive-vr', sessionInit ).then( onSessionStarted );
  
  				} else {
  
  					currentSession.end();
  
  				}
  
  			};
  
  		}
  
  		function disableButton() {
  
  			button.style.display = '';
  
  			button.style.cursor = 'auto';
  			button.style.left = 'calc(50% - 75px)';
  			button.style.width = '150px';
  
  			button.onmouseenter = null;
  			button.onmouseleave = null;
  
  			button.onclick = null;
  
  		}
  
  		function showWebXRNotFound() {
  
  			disableButton();
  
  			button.textContent = 'VR NOT SUPPORTED';
  
  		}
  
  		function showVRNotAllowed( exception ) {
  
  			disableButton();
  
  			console.warn( 'Exception when trying to call xr.isSessionSupported', exception );
  
  			button.textContent = 'VR NOT ALLOWED';
  
  		}
  
  		function stylizeElement( element ) {
  
  			element.style.position = 'absolute';
  			element.style.bottom = '20px';
  			element.style.padding = '12px 6px';
  			element.style.border = '1px solid #fff';
  			element.style.borderRadius = '4px';
  			element.style.background = 'rgba(0,0,0,0.1)';
  			element.style.color = '#fff';
  			element.style.font = 'normal 13px sans-serif';
  			element.style.textAlign = 'center';
  			element.style.opacity = '0.5';
  			element.style.outline = 'none';
  			element.style.zIndex = '999';
  
  		}
  
  		if ( 'xr' in navigator ) {
  
  			button.id = 'VRButton';
  			button.style.display = 'none';
  
  			stylizeElement( button );
  
  			navigator.xr.isSessionSupported( 'immersive-vr' ).then( function ( supported ) {
  
  				supported ? showEnterVR() : showWebXRNotFound();
  
  				if ( supported && VRButton.xrSessionIsGranted ) {
  
  					button.click();
  
  				}
  
  			} ).catch( showVRNotAllowed );
  
  			return button;
  
  		} else {
  
  			const message = document.createElement( 'a' );
  
  			if ( window.isSecureContext === false ) {
  
  				message.href = document.location.href.replace( /^http:/, 'https:' );
  				message.innerHTML = 'WEBXR NEEDS HTTPS'; // TODO Improve message
  
  			} else {
  
  				message.href = 'https://immersiveweb.dev/';
  				message.innerHTML = 'WEBXR NOT AVAILABLE';
  
  			}
  
  			message.style.left = 'calc(50% - 90px)';
  			message.style.width = '180px';
  			message.style.textDecoration = 'none';
  
  			stylizeElement( message );
  
  			return message;
  
  		}
  
  	}
  
  	static xrSessionIsGranted = false;
  
  	static registerSessionGrantedListener() {
  
  		if ( 'xr' in navigator ) {
  
  			// WebXRViewer (based on Firefox) has a bug where addEventListener
  			// throws a silent exception and aborts execution entirely.
  			if ( /WebXRViewer\//i.test( navigator.userAgent ) ) return;
  
  			navigator.xr.addEventListener( 'sessiongranted', () => {
  
  				VRButton.xrSessionIsGranted = true;
  
  			} );
  
  		}
  
  	}
  
  }
  
  VRButton.registerSessionGrantedListener();
  
  export { VRButton };
  