setupLesson = function ( canvas ) {

		// only once
		setupLesson = function () {};

		if ( canvas ) {

			canvas.addEventListener( 'webglcontextlost', function () {

				// the default is to do nothing. Preventing the default
				// means allowing context to be restored
				// e.preventDefault();  // can't do this because firefox bug - https://bugzilla.mozilla.org/show_bug.cgi?id=1633280
				sendMessage( {
					type: 'lostContext',
				} );

			} );

		}

	}
Gets a WebGL context.
makes its backing store the size it is displayed.
@param {OffscreenCanvas} canvas a canvas element.
@memberOf module:webgl-utils