如何在chart.js中显示图例项的工具提示

var ctx = document.getElementById('myChart').getContext('2d');
var myChart = new Chart(ctx, {
    type: 'bar',
    data: {
        labels: ['Red', 'Blue', 'Yellow', 'Green', 'Purple', 'Orange'],
        datasets: [{
            label: '# of Votes',
            data: [12, 19, 3, 5, 2, 3],
            backgroundColor: [
                'rgba(255, 99, 132, 0.2)',
                'rgba(54, 162, 235, 0.2)',
                'rgba(255, 206, 86, 0.2)',
                'rgba(75, 192, 192, 0.2)',
                'rgba(153, 102, 255, 0.2)',
                'rgba(255, 159, 64, 0.2)'
            ],
            borderColor: [
                'rgba(255, 99, 132, 1)',
                'rgba(54, 162, 235, 1)',
                'rgba(255, 206, 86, 1)',
                'rgba(75, 192, 192, 1)',
                'rgba(153, 102, 255, 1)',
                'rgba(255, 159, 64, 1)'
            ],
            borderWidth: 1
        }]
    },
    options: {
        tooltips: {
            enabled: true,
            backgroundColor: 'rgba(0, 0, 0, 0.8)',
            borderColor: 'rgba(0, 0, 0, 1)',
            borderWidth: 1,
            titleFontSize: 14,
            bodyFontSize: 12,
            callbacks: {
                label: function(tooltipItem, data) {
                    var label = data.labels[tooltipItem.index];
                    var value = data.datasets[tooltipItem.datasetIndex].data[tooltipItem.index];
                    return label + ': ' + value;
                }
            }
        }
    }
});