jointjs documentation
var graph = new joint.dia.Graph
var paper = new joint.dia.Paper({
el: $('#paper'),
width: 600,
height: 400,
gridSize: 10,
model: graph
});
var rect = new joint.shapes.basic.Rect({
position: { x: 50, y: 70 },
size: { width: 100, height: 40 }
});
graph.addCell(rect);