Question

我正在尝试学习使用Chartjs，当我尝试通过其ID获取canvas元素时，我遇到了一个问题。由于某种原因，它没有被定义。这是因为我正在调用document.getElementByID并且这不是在HTML文件中运行的吗？我试图使用外部文件来托管我的所有JS，而不是混乱我的HTML文件。

错误讯息： Uncaught TypeError: undefined is not a function

在chart-option.js的第2行找到：var ctx = document.getElementByID("sessions-graph").getContext("2d");

的index.html

<!doctype html>
<html>

    <head>
        <title>Google Super Proxy Test</title>
        <script src="Chart.min.js"></script>
        <script src="chart-options.js"></script>
    </head>

<body>

    <div style="width: 50%">
        <canvas id="sessions-graph" height="450" width="600"></canvas>
    </div>


</body>

</html>

图表-options.js

// Get the context of the canvas element
var ctx = document.getElementByID("sessions-graph").getContext("2d");
var sessionsGraph = new Chart(ctx).Bar(data); //Create a chart with "data" array

var data = {
    labels: ["January", "February", "March", "April", "May", "June", "July"],
    datasets: [
        {
            label: "My First dataset",
            fillColor: "rgba(220,220,220,0.5)",
            strokeColor: "rgba(220,220,220,0.8)",
            highlightFill: "rgba(220,220,220,0.75)",
            highlightStroke: "rgba(220,220,220,1)",
            data: [65, 59, 80, 81, 56, 55, 40]
        },
        {
            label: "My Second dataset",
            fillColor: "rgba(151,187,205,0.5)",
            strokeColor: "rgba(151,187,205,0.8)",
            highlightFill: "rgba(151,187,205,0.75)",
            highlightStroke: "rgba(151,187,205,1)",
            data: [28, 48, 40, 19, 86, 27, 90]
        }
    ]
};


Chart.defaults.global = {

    //Boolean - Whether the scale should start at zero, or an order of magnitude down from the lowest value
    scaleBeginAtZero : true,

    //Boolean - Whether grid lines are shown across the chart
    scaleShowGridLines : true,

    //String - Colour of the grid lines
    scaleGridLineColor : "rgba(0,0,0,.05)",

    //Number - Width of the grid lines
    scaleGridLineWidth : 1,

    //Boolean - If there is a stroke on each bar
    barShowStroke : true,

    //Number - Pixel width of the bar stroke
    barStrokeWidth : 2,

    //Number - Spacing between each of the X value sets
    barValueSpacing : 5,

    //Number - Spacing between data sets within X values
    barDatasetSpacing : 1

}

Answer 1

您的代码有拼写错误，方法应为document.getElementById()

尝试获取Canvas时未捕获的TypeError

1 个答案: