Live streaming data using chart.js, javascript, html

Question

I wanted to stream live data in the form of a chart. I'm new to Javascript, so I wanted to first experiment with the sample on this page. https://web.archive.org/web/20211113012042/https://nagix.github.io/chartjs-plugin-streaming/latest/samples/charts/line-horizontal.html

The code is given as:

var chartColors = {
    red: 'rgb(255, 99, 132)',
    orange: 'rgb(255, 159, 64)',
    yellow: 'rgb(255, 205, 86)',
    green: 'rgb(75, 192, 192)',
    blue: 'rgb(54, 162, 235)',
    purple: 'rgb(153, 102, 255)',
    grey: 'rgb(201, 203, 207)'
};

function randomScalingFactor() {
    return (Math.random() > 0.5 ? 1.0 : -1.0) * Math.round(Math.random() * 100);
}

function onRefresh(chart) {
    chart.config.data.datasets.forEach(function(dataset) {
        dataset.data.push({
            x: Date.now(),
            y: randomScalingFactor()
        });
    });
}

var color = Chart.helpers.color;
var config = {
    type: 'line',
    data: {
        datasets: [{
            label: 'Dataset 1 (linear interpolation)',
            backgroundColor: color(chartColors.red).alpha(0.5).rgbString(),
            borderColor: chartColors.red,
            fill: false,
            lineTension: 0,
            borderDash: [8, 4],
            data: []
        }, {
            label: 'Dataset 2 (cubic interpolation)',
            backgroundColor: color(chartColors.blue).alpha(0.5).rgbString(),
            borderColor: chartColors.blue,
            fill: false,
            cubicInterpolationMode: 'monotone',
            data: []
        }]
    },
    options: {
        title: {
            display: true,
            text: 'Line chart (hotizontal scroll) sample'
        },
        scales: {
            xAxes: [{
                type: 'realtime'
            }],
            yAxes: [{
                scaleLabel: {
                    display: true,
                    labelString: 'value'
                }
            }]
        },
        tooltips: {
            mode: 'nearest',
            intersect: false
        },
        hover: {
            mode: 'nearest',
            intersect: false
        },
        plugins: {
            streaming: {
                duration: 20000,
                refresh: 1000,
                delay: 2000,
                onRefresh: onRefresh
            }
        }
    }
};

window.onload = function() {
    var ctx = document.getElementById('myChart').getContext('2d');
    window.myChart = new Chart(ctx, config);
};

document.getElementById('randomizeData').addEventListener('click', function() {
    config.data.datasets.forEach(function(dataset) {
        dataset.data.forEach(function(dataObj) {
            dataObj.y = randomScalingFactor();
        });
    });
    window.myChart.update();
});

var colorNames = Object.keys(chartColors);
document.getElementById('addDataset').addEventListener('click', function() {
    var colorName = colorNames[config.data.datasets.length % colorNames.length];
    var newColor = chartColors[colorName];
    var newDataset = {
        label: 'Dataset ' + (config.data.datasets.length + 1),
        backgroundColor: color(newColor).alpha(0.5).rgbString(),
        borderColor: newColor,
        fill: false,
        lineTension: 0,
        data: []
    };

    config.data.datasets.push(newDataset);
    window.myChart.update();
});

document.getElementById('removeDataset').addEventListener('click', function() {
    config.data.datasets.pop();
    window.myChart.update();
});

document.getElementById('addData').addEventListener('click', function() {
    onRefresh(window.myChart);
    window.myChart.update();
});

<head>
    <script src="https://cdnjs.cloudflare.com/ajax/libs/moment.js/2.22.2/moment.min.js"></script>
    <script src="https://cdnjs.cloudflare.com/ajax/libs/Chart.js/2.7.2/Chart.min.js"></script>
    <script src="https://github.com/nagix/chartjs-plugin-streaming/releases/download/v1.5.0/chartjs-plugin-streaming.min.js"></script>
</head>
<body>
    <div>
        <canvas id="myChart"></canvas>
    </div>
    <p>
        <button id="randomizeData">Randomize Data</button>
        <button id="addDataset">Add Dataset</button>
        <button id="removeDataset">Remove Dataset</button>
        <button id="addData">Add Data</button>
    </p>
</body>

When I copy and paste it into jsfiddle, the first code snippet going into the Javascript section and the second going into the HTML section. However, nothing happens? Could someone explain why/help me edit it so that it works?

Note: the code above is not my own, it belongs to this guy

the snippet posted above works here, as for jsfiddle, i don't think it recognizes window.onload, if you draw the chart outside of onload it works --> https://jsfiddle.net/WhiteHat/dmfgvn7u/1/ — WhiteHat
– WhiteHat, Commented Jul 27, 2018 at 18:00

nagix · Accepted Answer · 2018-08-01 07:37:41Z

2

In JSFiddle, the load type is set to 'On Load' by default, so you cannot handle the load event. Setting the load type to 'No wrap - bottom of ' works (in the pop-up menu in the Javascript section).

answered Aug 1, 2018 at 7:37

nagix

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