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How to Add Chart.js Legends In Ember.js?

4 minutes read

To add chart.js legends in Ember.js, you can achieve this by adding the legend configuration option to the chart options when creating a chart using the chart.js library in your Ember.js application. The legend configuration allows you to customize the appearance and position of the legend in your chart. You can specify options such as the position, labels, and styles of the legend to suit your requirements. By including the legend configuration in your chart options, you can easily display a legend for your chart in your Ember.js application.


What is the syntax for adding legends in chart.js in ember.js?

To add legends in Chart.js in Ember.js, you can use the following syntax:


First, in your component template file (e.g. charts.hbs), you can add a canvas element to hold the chart and a div element to display the legend:

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<canvas id="myChart"></canvas>
<div id="legend"></div>


Next, in your component JavaScript file (e.g. charts.js), you can create the chart and add a legend using Chart.js options:

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import Component from '@ember/component';
import { on } from '@ember/object/evented';
import Chart from 'chart.js';

export default Component.extend({
  didInsertElement() {
    this._super(...arguments);

    let ctx = this.element.querySelector('#myChart').getContext('2d');

    let data = {
      labels: ['January', 'February', 'March', 'April', 'May', 'June', 'July'],
      datasets: [{
        label: 'My Dataset',
        data: [65, 59, 80, 81, 56, 55, 40],
        backgroundColor: 'blue'
      }]
    };

    let options = {
      legend: {
        display: false // hide the default legend
      },
      plugins: {
        beforeDraw: function(chart) {
          let legend = chart.chart.legend;
          legend.innerHTML = '';
          chart.data.datasets.forEach(function(dataset, i) {
            let label = document.createElement('div');
            label.style.display = 'inline-block';
            label.style.marginRight = '10px';
            label.innerHTML = '<span style="background-color:' + dataset.backgroundColor + '">&nbsp;&nbsp;&nbsp;</span> ' + dataset.label;
            legend.appendChild(label);
          });
        }
      }
    };

    let myChart = new Chart(ctx, {
      type: 'bar',
      data: data,
      options: options
    });

    let legend = this.element.querySelector('#legend');
    legend.innerHTML = myChart.generateLegend();
  }
});


In this code snippet, we first get the canvas context and define the chart data and options. We then customize the legend display using the plugins option and add a legend component using the generateLegend() method.


Finally, make sure to import the necessary dependencies such as Chart.js and ember.


Remember to customize the code to fit your specific chart and data requirements.


How to position legends in chart.js in ember.js?

In Ember.js, you can position legends in a Chart.js chart by setting the options property of the chart component. Here's an example of how to do this:

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// app/components/chart-component.js

import Component from '@glimmer/component';
import { action } from '@ember/object';

export default class ChartComponent extends Component {
  @action
  renderChart() {
    let ctx = this.element.querySelector('canvas').getContext('2d');
    let data = {
      labels: ['January', 'February', 'March', 'April', 'May'],
      datasets: [
        {
          label: 'Sales',
          data: [10, 20, 30, 40, 50],
          backgroundColor: 'rgba(255, 99, 132, 0.2)',
          borderColor: 'rgba(255, 99, 132, 1)',
          borderWidth: 1
        }
      ]
    };

    let options = {
      legend: {
        position: 'top' // Change the position of the legend here
      }
    };

    new Chart(ctx, {
      type: 'line',
      data: data,
      options: options
    });
  }
}


In this example, we set the position property of the legend object in the options object to 'top' to position the legend at the top of the chart. Other possible values for the position property are 'bottom', 'left', and 'right'.


You can further customize the styling and display of the legend by adding additional configuration options to the legend object in the options object. Refer to the Chart.js documentation for more details on available legend options and customization options.


How to show/hide specific legends in chart.js in ember.js?

In order to show/hide specific legends in a chart.js chart in Ember.js, you can achieve this by accessing the chart object from the chartjs library and updating the datasets array. Here is an example of how you can show and hide a specific legend in a chart:

  1. First, you need to create a chart using the ember-cli-chart library and initialize it in your component or controller:
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import Ember from 'ember';
import ChartComponent from 'ember-cli-chart/components/ember-chart';

export default ChartComponent.extend({
  tagName: 'canvas',
  classNames: ['my-chart'],

  didInsertElement() {
    this._super();
    let ctx = this.get('element').getContext('2d');
    let data = {
      labels: ['January', 'February', 'March', 'April', 'May', 'June', 'July'],
      datasets: [
        {
          label: 'Dataset 1',
          data: [12, 19, 3, 5, 2, 3, 7],
          backgroundColor: 'red'
        },
        {
          label: 'Dataset 2',
          data: [7, 20, 12, 21, 8, 12, 18],
          backgroundColor: 'blue'
        }
      ]
    };
    let options = {
      legend: {
        display: true
      }
    };
    let chart = new Chart(ctx, {
      type: 'bar',
      data: data,
      options: options
    });
    this.set('chart', chart);
  }
});


  1. Now, in order to show/hide a specific legend in the chart, you can use the legend.labels property in the chart object. For example, you can hide the legend for 'Dataset 2' by updating the chart object in your component's action or controller:
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actions: {
  hideLegend() {
    let chart = this.get('chart');
    chart.data.datasets.forEach((dataset, index) => {
      if (dataset.label === 'Dataset 2') {
        dataset.hidden = true;
      }
    });
    chart.update();
  }
}


  1. To show the hidden legend again, you can update the dataset.hidden property back to false:
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actions: {
  showLegend() {
    let chart = this.get('chart');
    chart.data.datasets.forEach((dataset, index) => {
      if (dataset.label === 'Dataset 2') {
        dataset.hidden = false;
      }
    });
    chart.update();
  }
}


By using the above approach, you can show/hide specific legends in a chart.js chart in Ember.js.

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