Synchronous file load
From JSXGraph Wiki
var board = JXG.JSXGraph.initBoard('jxgbox');
JXG.FileReader.parseFileContent('//jsxgraph.org/geonext/point.ggb', board, 'GeoGebra', false);
board.create('point',[0,0], {fixed:true, name:'jsxpoint1', size:1});
var J = JXG.getReference(board, "jsxpoint1");
var G = JXG.getReference(board, "geogebrapoint1");
J.setAttribute({size: 5});
G.setAttribute({size: 10});
board.setBoundingBox([-5, 5, 5, -5], true);