GoJS `diagram.model.toJson()` is not not updating after change

Question

I am using SvelteKit and GoJS

I've declared let diagram; before onMount(), and defined diagram = new go.Diagram('Diagram'); inside onMount() and all other details after that, including:

diagram.addModelChangedListener((e) => {
            if (e.isTransactionFinished) {
                saveDiagramToLocalStorage(); 
            }
});

saveDiagramToLocalStorage(); is defined after onMount():

const saveDiagramToLocalStorage = () => {
        const modelAsJson = diagram.model.toJson();
        console.log('SaveDiagram', modelAsJson);    // no changes on current data
        localStorage.setItem('myDiagramModel', modelAsJson);
};

And its all working fine, the function saveDiagramToLocalStorage() is beeing called, but,

The issue is:

diagram.model.toJson(); is always returning the same data, in other words is not being updated after changes in diagram.

Except:

Adding new node or link. The new ones are added, but the existing ones are still not updated. (I'm calling diagram.selection.<some_data> and that's well updated, but the diagram.model.toJson() is not picking changes on the existing ones for some reason)

I've tried:

• putting Diagram.rebuildParts() before diagram.model.toJson();
• putting saveDiagramToLocalStorage() inside onMount

Answer 1

It was a binding issue

Do not use this for binding:

.bind('location', 'loc', go.Point.parse).makeTwoWay(go.Point.stringify)

Always use go.GraphObject.make and makeTwoWay in your diagram.nodeTemplate to keep diagram.model fully updated with this kind of binding:

new go.Binding('location', 'loc', go.Point.parse).makeTwoWay(go.Point.stringify)

Full context: (working example)

// +page.svelte / <script>
onMount(() => {
    const $ = go.GraphObject.make;
    diagram = $(go.Diagram, DiagramDiv);

    diagram.nodeTemplate = $(
        go.Node,
        'Auto',
        {
            width: 50,
            height: 50
        },
        new go.Binding('location', 'loc', go.Point.parse).makeTwoWay(go.Point.stringify)
    )
});