var init = function() {
    //.. do some overall initialization
    $.ajax({
        url: '/url/',
        method: 'GET',
        dataType: 'json',
        data: {},  //probably you have some parameters
        success: displaygraph,
        error: function() {alert('error getting data');}
    });
}

var displaygraph = function(data) {
    $('#cy').cytoscape({
        style: // ...

        elements: {
            nodes: data.nodes,
            edges: data.edges
        },

        ready: function(){
            //...
        }
    });

}