[Chartjs]-Chart not rendering w/Chart.js on button click

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The documentation for the update function reads:

Triggers an update of the chart. This can be safely called after updating the data object. This will update all scales, legends, and then re-render the chart.

So you have to update the data object instead of passing the updated data objects in the update method. The method accepts only these properties:

  • duration
  • lazy
  • easing

In your sample you would have to change the following code:

myChart.update({
   type: chartType,
   data: chartData
});

to

myChart.type = chartType;
myChart.data = chartData;
myChart.update();

Below is your snippet with the change:

// /public/main.js
const chartData = {
  labels: ["Red", "Blue", "Yellow", "Green", "Purple", "Orange"],
  datasets: [{
    label: '# of Votes',
    data: [12, 19, 3, 16, 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)'
    ]
  }]
};
const barOptions = {
  scales: {
    yAxes: [{
      ticks: {
        beginAtZero: true
      }
    }]
  }
};

const ctx = document.getElementById("myChart").getContext('2d');

const myChart = new Chart(ctx, {
  type: 'bar',
  data: chartData,
  options: barOptions
});
// Get Chart Info from form

$(document).ready(function() {
  $("#render_btn").on("click", function(e) {
    e.preventDefault();

    // First grab form data off the page
    const formData = $("form").serializeArray();
    // Get Chart Type Seperate from Form Data
    const chartType = document.getElementById('chart_type').value;

    // Create a data Object for Chart constructor to use
    const chartData = {
      datasets: []
    };
    let datasetsItem = {};

    // Convert formData array to chartData object
    formData.forEach(function(value, index) {
      if (formData[index].name == 'labels') {
        chartData[(formData[index].name)] = formData[index].value;
      } else {
        datasetsItem[formData[index].name] = formData[index].value;
        chartData.datasets[0] = datasetsItem;
      }
    });

    // Now we have to do some converting i.e., chartData.labels must be
    // converted to array from string etc
    chartData.datasets[0].backgroundColor = splitString(chartData.datasets[0].backgroundColor);
    chartData.datasets[0].data = strToNumberArray(chartData.datasets[0].data);
    chartData.labels = splitString(chartData.labels);

    // Check if succesful
    try {
      if (!(chartData.datasets[0].backgroundColor) || !(chartData.datasets[0].data) || !(chartData.labels)) {
        throw new Error("Input Error. Recheck your form data.");
      }
      
      myChart.type = chartType;
      myChart.data = chartData;
      myChart.update();
    } catch (error) {
      alert(error);
    }


    // ============================================================= //
    // ============= Function definitions ========================== //
    // ============================================================= //
    function splitString(strToSplit, separator = ',') {
      if (strToSplit === undefined) {
        console.log("Error: splitString is empty.");
        return "";
      }

      // Test for a comma in the string
      const result = /,+/.test(strToSplit);
      if (!result) {
        alert(`Comma delimiter missing from ${strToSplit}`);
        return false;
      }

      // Split a string into an array and trim any whitespace
      let arrayOfStrings = strToSplit.split(separator);
      arrayOfStrings.forEach(function(value, index) {
        arrayOfStrings[index] = value.trim();
      });

      return arrayOfStrings;
    }

    // Function to convert string to an array then convert each element to a number
    function strToNumberArray(str, separator = ',') {
      if (str === undefined) {
        alert('Error: string is empty.');
        return "";
      }
      // Test for a comma in the string
      const result = /,+/.test(str);
      if (!result) {
        alert(`Comma delimiter missing from ${str}`);
        return false;
      }

      let arrayOfNumbers = str.split(separator).map(Number);

      return arrayOfNumbers;
    }

    // ============================================================== //
    // ================== End Function Definitions ================== //
    // ============================================================== //
  }); // .on "click"
});
<script src="https://code.jquery.com/jquery-3.2.1.min.js" integrity="sha256-hwg4gsxgFZhOsEEamdOYGBf13FyQuiTwlAQgxVSNgt4=" crossorigin="anonymous"></script>

<script src="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/js/bootstrap.min.js" integrity="sha384-Tc5IQib027qvyjSMfHjOMaLkfuWVxZxUPnCJA7l2mCWNIpG9mGCD8wGNIcPD7Txa" crossorigin="anonymous"></script>

<script src="https://cdnjs.cloudflare.com/ajax/libs/Chart.js/2.7.1/Chart.bundle.min.js"></script>

<canvas id="myChart" width="400" height="400"></canvas>

<h2>Input your values:</h2>
<!-- Chart Input Form -->
<!-- We dont want chart_type as part of form when we use serializeArray
        gather the data and use in chartData object -->
<div class="row">
  <div class="col-md-4 col-md-offset-4">
    <div class="form-group">
      <label for="chart_type">Chart Type</label>
      <input type="text" name="type" class="form-control" id="chart_type" placeholder="Chart Type">
    </div>
  </div>
</div>

<form>
  <div class="row">
    <div class="col-md-4 col-md-offset-4">
      <div class="form-group">
        <label for="chart_Label">Chart Label</label>
        <input type="text" name="label" class="form-control" id="chart_Label" placeholder="Chart Label">
      </div>
    </div>
  </div>

  <div class="row">
    <div class="col-md-6 col-md-offset-4">
      <div class="form-group">
        <label for="chart_labels">Chart Labels</label>
        <input type="text" name="labels" class="form-control" id="chart_labels" placeholder="Apr, May, June Note:Seperated by Commas">
      </div>
    </div>
  </div>

  <div class="row">
    <div class="col-md-6 col-md-offset-4">
      <div class="form-group">
        <label for="chart_data">Chart Data</label>
        <input type="text" name="data" class="form-control" id="chart_data" placeholder="i.e., 25 44 60 etc">
      </div>
    </div>
  </div>

  <div class="row">
    <div class="col-md-6 col-md-offset-4">
      <div class="form-group">
        <label for="chart_colors">Chart Colors</label>
        <input type="text" name="backgroundColor" class="form-control" id="chart_colors" placeholder="i.e., red, blue, yellow, purple">
      </div>
    </div>
  </div>
  <div class="row">
    <div class="col-md-4 col-md-offset-5">
      <button class="btn btn-primary btn-lg" id="render_btn">Render Graph</button>
    </div>
  </div>
</form>

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