Chart.js v2: How to make tooltips always appear on pie chart?

Question

I have found similar questions in Stack Overflow, but all of them were addressed one and two years ago. Now Chart.js has come up in version 2, and lots of the documentation

Answer 1

With the new Chart.js 2.1 you can write a plugin to do this and control it via an options property

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Preview

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Script

Note that you need to register the plugin before you initialize the chart

Chart.pluginService.register({
    beforeRender: function (chart) {
        if (chart.config.options.showAllTooltips) {
            // create an array of tooltips
            // we can't use the chart tooltip because there is only one tooltip per chart
            chart.pluginTooltips = [];
            chart.config.data.datasets.forEach(function (dataset, i) {
                chart.getDatasetMeta(i).data.forEach(function (sector, j) {
                    chart.pluginTooltips.push(new Chart.Tooltip({
                        _chart: chart.chart,
                        _chartInstance: chart,
                        _data: chart.data,
                        _options: chart.options,
                        _active: [sector]
                    }, chart));
                });
            });

            // turn off normal tooltips
            chart.options.tooltips.enabled = false;
        }
    },
    afterDraw: function (chart, easing) {
        if (chart.config.options.showAllTooltips) {
            // we don't want the permanent tooltips to animate, so don't do anything till the animation runs atleast once
            if (!chart.allTooltipsOnce) {
                if (easing !== 1)
                    return;
                chart.allTooltipsOnce = true;
            }

            // turn on tooltips
            chart.options.tooltips.enabled = true;
            Chart.helpers.each(chart.pluginTooltips, function (tooltip) {
                tooltip.initialize();
                tooltip.update();
                // we don't actually need this since we are not animating tooltips
                tooltip.pivot();
                tooltip.transition(easing).draw();
            });
            chart.options.tooltips.enabled = false;
        }
    }
});

and then

new Chart(ctx, {
    type: 'pie',
    data: data,
    options: {
        showAllTooltips: true
        ...

With the older 2.x version, you should able to move the same (or similar, I'm not sure about the earlier data structure ) to the options.animation.onComplete

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Fiddle - http://jsfiddle.net/q15ta78q/