How to have different values for the chart and the tooltip in chart.js?

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by dana , in category: Javascript , 2 months ago

How to have different values for the chart and the tooltip in chart.js?

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1 answer

by aniya.jaskolski , 2 months ago

@dana 

To have different values for the chart and the tooltip in Chart.js, you can use the built-in tooltip callbacks provided by Chart.js.


Here's an example of how to achieve this:

  1. Define your chart data:
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var chartData = {
  labels: ['January', 'February', 'March', 'April', 'May', 'June'],
  datasets: [{
    label: 'Sales',
    data: [100, 200, 150, 250, 180, 300],
    backgroundColor: 'rgba(0, 123, 255, 0.4)',
    borderColor: 'rgba(0, 123, 255, 1)',
    borderWidth: 1
  }]
};


  1. Define your chart options and set the tooltip callback:
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var chartOptions = {
  tooltips: {
    callbacks: {
      label: function(tooltipItem, data) {
        // Get the chart's dataset
        var dataset = data.datasets[tooltipItem.datasetIndex];
        // Calculate the tooltip value based on the actual dataset value
        var value = dataset.data[tooltipItem.index] * 2;
        // Return the custom tooltip value
        return value;
      }
    }
  }
};


In this example, the tooltip callback function retrieves the dataset value and then calculates a different value for the tooltip. You can modify the logic inside the callback function according to your needs.

  1. Create the chart using the defined data and options:
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var ctx = document.getElementById('myChart').getContext('2d');
var myChart = new Chart(ctx, {
  type: 'bar',
  data: chartData,
  options: chartOptions
});


In this example, a bar chart is being created, but you can replace it with any other chart type (e.g., line, pie, etc.).


With this approach, the chart will display the original data values, while the tooltips will show the different values calculated in the callback function.