图表区JS v2:如何设置单位？

<script src="chartjs.min.js"></script>

var myChart = new Chart(ctx, {
    type: 'bar',
    data: {
        labels: ['January', 'February', 'March', 'April', 'May', 'June', 'July'],
        datasets: [{
            label: 'Sales',
            data: [12, 19, 3, 5, 2, 3, 10]
        }]
    },
    options: {
        // 设置单位
        scales: {
            y: {
                beginAtZero: true,
                ticks: {
                    callback: function(value, index, values) {
                        return value + ' 单位';
                    }
                }
            }
        }
    }
});

options: {
    title: {
        display: true,
        text: 'Monthly Sales'
    },
    // 其他配置项
}