Chart.js data values from textbox input only load once-CodePudding

I'm trying to learn chart.js and have the following code that displays a graph.

However, it only loads the data once. If I change the values in the textbox inputs and click the button again, it doesn't change the chart at all.

I tried playing with the info here: https://www.chartjs.org/docs/latest/developers/updates.html but just can't get it to work.

function graphGraph() {

    let R = document.getElementById("RedVal").value;
    let B = document.getElementById("BlueVal").value;
    let Y = document.getElementById("YellowVal").value;
    let G = document.getElementById("GreenVal").value;
    let P = document.getElementById("PurpleVal").value;
    let O = document.getElementById("OrangeVal").value;

    let ctx = document.getElementById('myChart').getContext('2d');
    let 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],
                data: [R, B, Y, G, P, O],
                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: {
            scales: {
                y: {
                    beginAtZero: true
                }
            }
        }
    });
}

<script src="https://cdn.jsdelivr.net/npm/chart.js"></script>
<div>
    <h3>Example Graph:</h3>
    <br />
    <table style="width:70%;" border="1" align="center">
        <tr>
            <th>Colour</th>
            <th>Value</th>
        </tr>
        <tr>
            <td>Red =</td>
            <td><input id="RedVal" min="0" type="text" /></td>
        </tr>
        <tr>
            <td>Blue =</td>
            <td><input id="BlueVal" min="0" type="text" /></td>
        </tr>
        <tr>
            <td>Yellow =</td>
            <td><input id="YellowVal" min="0" type="text" /></td>
        </tr>
        <tr>
            <td>Green =</td>
            <td><input id="GreenVal" min="0" type="text" /></td>
        </tr>
        <tr>
            <td>Purple =</td>
            <td><input id="PurpleVal" min="0" type="text" /></td>
        </tr>
        <tr>
            <td>Orange =</td>
            <td><input id="OrangeVal" min="0" type="text" /></td>
        </tr>
    </table>
</div>

<div>
    <input id="graphGraph" type="button" value="graphGraph" onclick="graphGraph()" />
    <canvas id="myChart"></canvas>
</div>

CodePudding user response：

As the error states the canvas is already in use so you would need to update it instead like so:

let myChart = undefined;

function graphGraph() {

  let R = document.getElementById("RedVal").value;
  let B = document.getElementById("BlueVal").value;
  let Y = document.getElementById("YellowVal").value;
  let G = document.getElementById("GreenVal").value;
  let P = document.getElementById("PurpleVal").value;
  let O = document.getElementById("OrangeVal").value;

  if (Chart.getChart(myChart) === undefined) {
    let ctx = document.getElementById('myChart').getContext('2d');
    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],
          data: [R, B, Y, G, P, O],
          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: {
        scales: {
          y: {
            beginAtZero: true
          }
        }
      }
    });
  } else {
    myChart.data.datasets[0].data = [R, B, Y, G, P, O];
    myChart.update();
  }
}

<script src="https://cdn.jsdelivr.net/npm/chart.js"></script>
<div>
  <h3>Example Graph:</h3>
  <br />
  <table style="width:70%;" border="1" align="center">
    <tr>
      <th>Colour</th>
      <th>Value</th>
    </tr>
    <tr>
      <td>Red =</td>
      <td><input id="RedVal" min="0" type="text" /></td>
    </tr>
    <tr>
      <td>Blue =</td>
      <td><input id="BlueVal" min="0" type="text" /></td>
    </tr>
    <tr>
      <td>Yellow =</td>
      <td><input id="YellowVal" min="0" type="text" /></td>
    </tr>
    <tr>
      <td>Green =</td>
      <td><input id="GreenVal" min="0" type="text" /></td>
    </tr>
    <tr>
      <td>Purple =</td>
      <td><input id="PurpleVal" min="0" type="text" /></td>
    </tr>
    <tr>
      <td>Orange =</td>
      <td><input id="OrangeVal" min="0" type="text" /></td>
    </tr>
  </table>
</div>

<div>
  <input id="graphGraph" type="button" value="graphGraph" onclick="graphGraph()" />
  <canvas id="myChart"></canvas>
</div>