Make the `chart.data.datasets.dataset.hidden` reflect the actual value

[szmarczak]

Feature Proposal

    chart.data.datasets = Object.keys(data[territorialUnit]).map(representationMethod => {
        const hidden = chart.data.datasets.find(entry => entry.label === representationMethod)?.hidden;

        return {
            label: representationMethod,
            data: Object.fromEntries(Object.entries(data[territorialUnit][representationMethod]).filter(filter)),
            borderWidth: 1,
            hidden: hidden ?? representationMethod !== defaultRepresentationMethod,
        };
    });

    chart.update();

The above is always resetting hidden to the default value (the !==), because dataset.hidden is not updated when user interacts.

I'm assigning datasets this way instead of .data = because I'm downloading the data asynchronously, so there's no initial data when the chart is created. I'm not checking if the dataset already exists, because in my opinion this would be unnecessary code.

Possible Implementation

No response

[stockiNail]

@szmarczak the hidden option is usually used in the chart configuration for initial status of the dataset. To check the dataset visibility, there is the isDatasetVisible chart API, see the following signature.

isDatasetVisible(datasetIndex: number): boolean;

Applying it to your code, it could be:

    chart.data.datasets = Object.keys(data[territorialUnit]).map(representationMethod => {
        const datasetIndex = chart.data.datasets.findIndex(entry => entry.label === representationMethod);
        const hidden = chart.isDatasetVisible(datasetIndex);
        return {
            label: representationMethod,
            data: Object.fromEntries(Object.entries(data[territorialUnit][representationMethod]).filter(filter)),
            borderWidth: 1,
            hidden: hidden || representationMethod !== defaultRepresentationMethod,
        };
    });

    chart.update();