Code

function toJsonString(diagram)
{
    var graph = { nodes:[], links: [] };
    var nodeCounter = 0;

    diagram.nodes.forEach(function (node)
    {
        node.jsonId = nodeCounter;
        graph.nodes.push({
            id: nodeCounter++,
            name: node.getText()
        });
    });

    diagram.links.forEach(function (link)
    {
        graph.links.push({
            origin: link.getOrigin().jsonId,
            target: link.getDestination().jsonId
        });
    });

    return Sys.Serialization.JavaScriptSerializer.serialize(graph);
}