在图表上使用鼠标选择间隔时，获取X轴上的起始值和结束值

// HTML
<canvas id="myChart"></canvas>

// JavaScript
var canvas = document.getElementById("myChart");
var ctx = canvas.getContext("2d");

// 初始化图表
var myChart = new Chart(ctx, {
    type: "line",
    data: {
        labels: ["Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"],
        datasets: [{
            label: "Sales",
            data: [100, 150, 200, 250, 300, 350, 400, 450, 500, 550, 600, 650],
            backgroundColor: "rgba(0, 123, 255, 0.5)",
            borderColor: "rgba(0, 123, 255, 1)",
            borderWidth: 1
        }]
    },
    options: {
        responsive: true,
        maintainAspectRatio: false,
        scales: {
            x: {
                display: true,
                title: {
                    display: true,
                    text: "Months"
                }
            },
            y: {
                display: true,
                title: {
                    display: true,
                    text: "Sales"
                }
            }
        }
    }
});

// 监听鼠标选择事件
canvas.addEventListener("mousedown", handleMouseDown);
canvas.addEventListener("mousemove", handleMouseMove);
canvas.addEventListener("mouseup", handleMouseUp);

// 记录鼠标坐标值
var startX, endX;

function handleMouseDown(event) {
    startX = event.clientX;
}

function handleMouseMove(event) {
    if (startX !== undefined) {
        endX = event.clientX;
    }
}

function handleMouseUp() {
    if (startX !== undefined && endX !== undefined) {
        // 根据起始值和结束值计算选择的间隔范围
        var startIndex = Math.floor(startX / (canvas.width / myChart.data.labels.length));
        var endIndex = Math.floor(endX / (canvas.width / myChart.data.labels.length));
        var selectedRange = myChart.data.labels.slice(startIndex, endIndex + 1);

        console.log("起始值：" + myChart.data.labels[startIndex]);
        console.log("结束值：" + myChart.data.labels[endIndex]);
        console.log("选择的间隔范围：" + selectedRange);
    }

    // 重置坐标值
    startX = undefined;
    endX = undefined;
}