jsTree - loading subnodes via ajax on demand

Question

I'm trying to get a jsTree working with on demand loading of subnodes. My code is this:

jQuery('#introspection_tree').jstree({ 
        "json_data" : {
            "ajax" : {
                url : "http://localhost/introspection/introspection/product"
            }
    },
    "plugins" : [ "themes", "json_data", "ui" ]
    });

The json returned from the call is

[
  {
    "data": "Kit 1",
    "attr": {
      "id": "1"
    },
    "children": [
      [
        {
          "data": "Hardware",
          "attr": {
            "id": "2"
          },
          "children": [

          ]
        }
      ],
      [
        {
          "data": "Software",
          "attr": {
            "id": "3"
          },
          "children": [

          ]
        }
      ]
    ]
  }
  .....
]

Each element could have a lot of children, the tree is going to be big. Currently this is loading the whole tree at once, which could take some time. What do I have to do to implement on-demand-loading of child-nodes when they are opened by the user?

Thanks in advance.

Answer 1

Irishka pointed me in the right direction, but does not fully resolve my problem. I fiddled around with her answer and came up with this. Using two different server functions is done only for clarity. The first one lists all products at top level, the second one lists all children of a given productid:

jQuery("#introspection_tree").jstree({
    "plugins" : ["themes", "json_data", "ui"],
    "json_data" : {
        "ajax" : {
            "type": 'GET',
            "url": function (node) {
                var nodeId = "";
                var url = ""
                if (node == -1)
                {
                    url = "http://localhost/introspection/introspection/product/";
                }
                else
                {
                    nodeId = node.attr('id');
                    url = "http://localhost/introspection/introspection/children/" + nodeId;
                }

                return url;
            },
            "success": function (new_data) {
                return new_data;
            }
        }
    }
});

The json data returned from the functions is like this (notice the state=closed in each node):

[
  {
    "data": "Kit 1",
    "attr": {
      "id": "1"
    },
    "state": "closed"
  },
  {
    "data": "KPCM 049",
    "attr": {
      "id": "4"
    },
    "state": "closed"
  },
  {
    "data": "Linux BSP",
    "attr": {
      "id": "8"
    },
    "state": "closed"
  }
]

No static data is needed, the tree is now fully dynamic on each level.