## Serialization

This is the third article of the intermediate section of the JointJS tutorial. Go back to events. Alternatively, you can return to index of all articles.

Data serialization is very easy in JointJS. It is done through two import/export functions on the Graph class:

- `graph.toJSON()` - converts the whole graph into a JSON object.
- `graph.fromJSON()` - overwrite current graph contents with converted contents of a provided JSON object.

### Persistence

The functions preserve all cells that have been added to the graph. Additionally, note that custom properties saved on the graph are preserved as well. You can use this to store additional state information:

    var graph1 = new joint.dia.Graph();
    graph1.set('graphCustomProperty', true);
    graph1.set('graphExportTime', Date.now());
    var jsonObject = graph1.toJSON();

    // transmission of `jsonObject` across network etc.

    var graph2 = new joint.dia.Graph(); // new empty graph
    graph2.fromJSON(jsonObject);
    graph2.get('graphCustomProperty'); // true
    graph2.get('graphExportTime'); // e.g. 627247800000

It is important to remember that the two functions work with JSON objects - not JSON strings. However, if necessary, you can easily convert back and forth using the native JavaScript `JSON.stringify()` and `JSON.parse()` functions:

    var graph1 = new joint.dia.Graph();
    var jsonObject = graph1.toJSON();
    var jsonString = JSON.stringify(jsonObject);

    // transmission of `jsonString` across network etc.

    var graph2 = new joint.dia.Graph(); // new empty graph
    graph2.fromJSON(JSON.parse(jsonString));

Depending on how you store/transmit your app data, you may work with the JSON objects directly (e.g. when storing it in a non-relational database like MongoDB), or in the stringified form (which can be stored anywhere plaintext can be stored, at the added cost of stringifying & parsing of the JSON object for every transmission).

### Synthetic Graphs

It is of course also possible to avoid using the `graph.toJSON()` function altogether and instead construct your own synthetic graphs; you just need to make sure that the object you provide is valid JSON and that it contains a `cells` array property:

    var graph = new joint.dia.Graph();
    graph.fromJSON({
        cells: [{
            id: 1,
            type: 'standard.Rectangle',
            position: {
                x: 100,
                y: 100
            },
            size: {
                width: 100,
                height: 100
            }
        }]
    });

The `cells` array can even be empty, if you want to create an empty synthetic graph:

    var graph = new joint.dia.Graph();
    graph.fromJSON({ cells: [] });

### Limitations

Keep in mind the general limitations of the JSON format. Some commonly used native JavaScript data types (including `Function`, `Date`, and `undefined`) are not supported. The variables that have values of these types will not be persisted. Among other things, this means that if persistence is important in your application, you should choose to define custom element/link subtypes instead of embedding custom functions into default `joint.dia.Element` and `joint.dia.Link` types.

Additionally, if you want to make use of the JSON objects and directly store them into MongoDB, you should remember its additional restriction on object keys starting with the `.` (dot) or `$` (dollar sign) symbols. Those are reserved for internal use of the MongoDB system. This is significant in the context of JointJS because it precludes the use of CSS-style selectors in the `attrs` arrays of your Elements and Links. Therefore, if persistence is important to you and you want to save data directly to MongoDB, you should always define custom subelement selectors in the markup of your custom elements instead of relying on CSS-style selectors.

In the next section of the intermediate tutorial, we will learn about creating custom elements.