Chart Js Cannot read property 'length' of undefined

Question

Using Chart js I am trying to pull data from Ajax call to supply to the Chart. I found a few other postings where people have suggested delaying the canvas load but nothing has seemed to work. Currently this is the what I have below and the error that I get is

$(function () {

GetChartData();

    function GetChartData() {
    $.ajax({
        url: ajaxURL,
        method: 'GET',
        dataType: 'json',
        success: function (d) {
            //-------------
            //- BAR CHART -
            //-------------
            var barChartData = d;
            var barChartCanvas = $("#barChart").get(0).getContext("2d");
            var barChart = new Chart(barChartCanvas);
            // console.log(datajson);
            //barChartData.datasets[1].fillColor = "#00a65a";
            //barChartData.datasets[1].strokeColor = "#00a65a";
            //barChartData.datasets[1].pointColor = "#00a65a";
            var barChartOptions = {
                //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 - Whether to show horizontal lines (except X axis)
                scaleShowHorizontalLines: true,
                //Boolean - Whether to show vertical lines (except Y axis)
                scaleShowVerticalLines: true,
                //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,
                multiTooltipTemplate: "<%=datasetLabel%>: <%= value + ' %' %>",
                //String - A legend template
                legendTemplate: "<ul class=\"<%=name.toLowerCase()%>-legend\"><% for (var i=0; i<datasets.length; i++){%><li><span style=\"background-color:<%=datasets[i].fillColor%>\"></span><%if(datasets[i].label){%><%=datasets[i].label%><%}%></li><%}%></ul>",
                //Boolean - whether to make the chart responsive
                responsive: true,
                maintainAspectRatio: true
            };


            barChartOptions.datasetFill = false;
            barChart.Bar(barChartData, barChartOptions);


        }
    });
    }
});

UPDATE HERE SHOWING HOW NON AJAX WORKS

The below code is taking the results of the Ajax get request (which I got from dumping it to the console) and creating a "hard coded" version of the same thing. The only thing that should technically be different is one has the data loaded at time of the page and the second the data is loaded very briefly after.

 var chartData = {
    "labels": [
      "April"
    ],
    "datasets": [
      {
          "label": "Not Sure What to Put Here",
          "fillColor": "#662B60",
          "strokeColor": "#662B60",
          "pointColor": "#662B60",
          "pointStrokeColor": "#662B60",
          "pointHighlightFill": "#662B60",
          "pointHighlightStroke": "#662B60",
          "data": [
            1
          ]
      },
      {
          "label": "Not Sure What to Put Here",
          "fillColor": "#88B56E",
          "strokeColor": "#88B56E",
          "pointColor": "#88B56E",
          "pointStrokeColor": "#88B56E",
          "pointHighlightFill": "#88B56E",
          "pointHighlightStroke": "#88B56E",
          "data": [
            1
          ]
      },
      {
          "label": "Not Sure What to Put Here",
          "fillColor": "#48CA2B",
          "strokeColor": "#48CA2B",
          "pointColor": "#48CA2B",
          "pointStrokeColor": "#48CA2B",
          "pointHighlightFill": "#48CA2B",
          "pointHighlightStroke": "#48CA2B",
          "data": [
            0.83
          ]
      }
    ]
};


    //-------------
    //- BAR CHART -
    //-------------
var barChartData = chartData;
    var barChartCanvas = $("#barChart").get(0).getContext("2d");
    var barChart = new Chart(barChartCanvas);

    //barChartData.datasets[1].fillColor = "#00a65a";
    //barChartData.datasets[1].strokeColor = "#00a65a";
    //barChartData.datasets[1].pointColor = "#00a65a";
    var barChartOptions = {
        //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 - Whether to show horizontal lines (except X axis)
        scaleShowHorizontalLines: true,
        //Boolean - Whether to show vertical lines (except Y axis)
        scaleShowVerticalLines: true,
        //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,
        multiTooltipTemplate: "<%=datasetLabel%>: <%= value + ' %' %>",
        //String - A legend template
        legendTemplate: "<ul class=\"<%=name.toLowerCase()%>-legend\"><% for (var i=0; i<datasets.length; i++){%><li><span style=\"background-color:<%=datasets[i].fillColor%>\"></span><%if(datasets[i].label){%><%=datasets[i].label%><%}%></li><%}%></ul>",
        //Boolean - whether to make the chart responsive
        responsive: true,
        maintainAspectRatio: true
    };


    barChartOptions.datasetFill = false;
    barChart.Bar(barChartData, barChartOptions);

Update I changed from the min version of chart.js to the full version so I could see where exactly it was erroring out at.

Here is the image from chrome console

Answer 1

The problem is that when your code executes, the canvas has not been created yet. You should wrap your code inside a function and assign that function to window.onload event. You can see the sample code below.

window.onload = function() {
  var ctx = document.getElementById("myChart");
  var lineChart = new Chart(ctx, {
    type: 'line',
    data: {
      labels: ["Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"],
      datasets: [{
        label: "2015",
        data: [10, 8, 6, 5, 12, 8, 16, 17, 6, 7, 6, 10]
      }]
    }
  })
}

<html>

<head>
  <script src="https://cdnjs.cloudflare.com/ajax/libs/Chart.js/2.5.0/Chart.js"></script>

</head>

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

</html>

Answer 2

Found the answer,

The Ajax results has to be parsed first.

resulting fix

var barChartData = JSON.parse(d);