How to Add A Vertical Cursor Line In Chart.js?

9 minutes read

To add a vertical cursor line in Chart.js, you can follow these steps:

  1. First, ensure that you have included the latest version of Chart.js in your project. You can download it from the Chart.js website or include it via a package manager like npm or yarn.
  2. Create a canvas element in your HTML where you want to render the chart:
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<canvas id="myChart"></canvas>


  1. Initialize and configure your chart using JavaScript. You can define your chart configuration options, including data, labels, colors, etc. For the purpose of adding a vertical cursor line, you can modify the options object as follows:
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var ctx = document.getElementById('myChart').getContext('2d');
var chart = new Chart(ctx, {
    type: 'line',
    data: {
        labels: ['January', 'February', 'March', 'April', 'May', 'June'],
        datasets: [{
            label: 'My Dataset',
            borderColor: 'rgb(75, 192, 192)',
            data: [0, 10, 5, 2, 20, 30],
        }]
    },
    options: {
        interaction: {
            mode: 'index', // Enable the cursor line
        },
        plugins: {
            tooltip: {
                intersect: false, // Prevent tooltip from being hidden
            },
            legend: {
                display: false, // Hide the legend (optional)
            }
        },
        scales: {
            x: {
                display: true,
            },
            y: {
                display: true,
            }
        },
    }
});


Here, the interaction section enables the cursor line by setting the mode to 'index'.

  1. You can further customize the appearance of the cursor line, tooltips, and other aspects based on your requirements. The example above also hides the legend and prevents the tooltip from being hidden when the cursor line is active.


That's it! With the above steps, you can add a vertical cursor line to your Chart.js chart. This line will display when you hover over the chart, providing an easy way to reference specific data points.

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What is chart.js?

Chart.js is a JavaScript library that enables users to create interactive and customizable charts and graphs on websites. It provides a simple and flexible API, supporting a wide range of chart types including bar charts, line charts, pie charts, doughnut charts, radar charts, and more. With Chart.js, developers can easily generate visually appealing data visualizations using HTML5 canvas.


Can multiple vertical cursor lines be added to a single chart in chart.js?

No, Chart.js does not have built-in support for multiple vertical cursor lines in a single chart. However, you can achieve this by extending Chart.js and customizing the functionality yourself. You would need to modify the source code, create a custom plugin, or use a third-party library that offers this feature.


How to display tooltips when hovering over a vertical cursor line in chart.js?

To display tooltips when hovering over a vertical cursor line in Chart.js, you can use custom plugin. Here is the code example:

  1. Create a new file called chart.tooltip.js and add the following code:
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Chart.plugins.register({
    afterEvent: function(chart, event, options) {
        var element = chart.getElementAtEvent(event)[0];

        if (element && element._model && element._model.x) {
            var tooltipModel = chart.tooltip._model;
            tooltipModel.x = element._model.x;
            tooltipModel.y = 0;
            tooltipModel.dataPoints = [element];
            chart.tooltip._options.enabled = true;
            chart.tooltip.initialize();
            chart.tooltip.update(true);
            chart.render();
        } else {
            chart.tooltip._options.enabled = false;
            chart.tooltip.update(true);
            chart.render();
        }
    }
});


  1. Include the chart.tooltip.js file in your HTML:
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<!DOCTYPE html>
<html>
<head>
    <meta charset="UTF-8">
    <title>Tooltip Example</title>
    <script src="https://cdn.jsdelivr.net/npm/chart.js"></script>
    <script src="chart.tooltip.js"></script>
</head>
<body>
    <canvas id="myChart"></canvas>
    
    <script>
        // Your chart.js initialization code goes here
    </script>
</body>
</html>


  1. Update your chart initialization code to include the hover and plugins options:
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var ctx = document.getElementById('myChart').getContext('2d');
var myChart = new Chart(ctx, {
    type: 'line',
    data: {
        labels: ['January', 'February', 'March', 'April', 'May', 'June', 'July'],
        datasets: [{
            label: 'My Dataset',
            data: [65, 59, 80, 81, 56, 55, 40]
        }]
    },
    options: {
        hover: {
            mode: 'nearest',
            intersect: false,
        },
        plugins: {
            tooltip: {
                enabled: false
            }
        }
    }
});


Now, when you hover over a vertical cursor line in the chart, a tooltip will be displayed.


How to include chart.js in my HTML?

To include Chart.js in your HTML page, you need to follow these steps:

  1. Download and save the latest version of Chart.js from the Chart.js website (https://www.chartjs.org/). You can choose either the full version or just the necessary chart type you require.
  2. Place the downloaded Chart.js file in a suitable location within your project directory.
  3. Open your HTML file and add a
  4. Once you have included the Chart.js file, you can start using it to create charts. You can define a element in your HTML and set a unique ID for it.
  5. In a separate JavaScript file or within a
  6. Save your HTML file and open it in a web browser. You should see the chart rendered on the page.


Note: Remember to include Chart.js before using it and ensure that your file paths and code syntax are correct.


What is the default color of a vertical cursor line in chart.js?

The default color of a vertical cursor line in Chart.js is usually a light gray color.

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