React ChartJS 2：点击图表获取数据

Question

I found many other questions on StackOverflow as well as GitHub but none of them worked for me...

I have a graph built using ChartJS. When I click on any of the bars(orange, green or red) I want to get the corresponding value. Is there any way to achieve this? The npm package I am using is react-chartjs-2. It has 2 props that I found may be helpful but don't know how to use it in this case. They are getElementsAtEvent and onElementsClick . These props when used gives tons of data except the value of the bar that I just clicked into.

This is how I import the component

import { Bar } from "react-chartjs-2";

This is how I use the component

<Bar
  data={barData}
  height={275}
  options={{
    maintainAspectRatio: false,
    scales: {
      yAxes: [
        {
          ticks: {
            beginAtZero: true,
          },
        },
      ],
    },
  }}
/>;

And the variable barData is as follows:

const barData = {
  labels: [
    "04-07-2020",
    "05-07-2020",
    "06-07-2020",
    "07-07-2020",
    "08-07-2020",
    "09-07-2020",
    "10-07-2020",
  ],

  datasets: [
    {
      label: "Cases",
      borderWidth: 1,
      backgroundColor: "#ffc299",
      borderColor: "#cc5200",
      hoverBackgroundColor: "#ed873e",
      hoverBorderColor: "#e35f00",
      data: [673165, 697413, 719664, 742417, 767296, 793802, 820916],
    },
    {
      label: "Recovered",
      borderWidth: 1,
      backgroundColor: "#b3ffb3",
      borderColor: "#00ff00",
      hoverBackgroundColor: "#55cf72",
      hoverBorderColor: "#2c9c46",
      data: [409083, 424433, 439934, 456831, 476378, 495513, 515386],
    },
    {
      label: "Deaths",
      borderWidth: 1,
      backgroundColor: "#de8078",
      borderColor: "#fa6457",
      hoverBackgroundColor: "#d73627",
      hoverBorderColor: "#ff4636",
      data: [19268, 19693, 20159, 20642, 21129, 21604, 22123],
    },
  ],
};

This is the graph

Any help is appreciated

Answer 1

Since your data is structured in a certain way, when a bar is clicked, an array of size 3 is returned as elem . You can extract the data from there based on your requirement.

Using onElementsClick :

<Bar
  data={barData}
  height={275}
  onElementsClick={elem => {
    var data = barData.datasets[elem[0]._datasetIndex].data;
    console.log("Cases", data[elem[0]._index]);

    data = barData.datasets[elem[1]._datasetIndex].data;
    console.log("Recovered", data[elem[1]._index]);

    data = barData.datasets[elem[2]._datasetIndex].data;
    console.log("Deaths", data[elem[2]._index]);
  }}
  options={{
    maintainAspectRatio: false,
    scales: {
      yAxes: [
        {
          ticks: {
            beginAtZero: true,
          },
        },
      ],
    },
  }}
/>;

elem is populated with the clicked element. You might need to tweak this code a bit to achieve exactly what you're looking for depending on what you want to do with that data. Sandbox in comment.

Answer 2

You can define an onClick function inside the chart options.

onClick: (event, elements) => {
  const chart = elements[0]._chart;
  const element = chart.getElementAtEvent(event)[0];
  const dataset = chart.data.datasets[element._datasetIndex];
  const xLabel = chart.data.labels[element._index];
  const value = dataset.data[element._index];
  console.log(dataset.label + " at " + xLabel + ": " + value);
}

Please have a look at your amended code in the followingStackBlitz .

Answer 3

It seems, that onElementsClick is deprecated in chart-js-2 ver.>3 You cat try this:

<Bar
  data={data}
  options={options}
  getElementAtEvent={(elements, event) => {
    if (event.type === "click" && elements.length) {
      console.log(elements[0]);
    }
  }}
/>