Charts #

Charts turn complex data into clear visuals, revealing trends and comparisons at a glance.

Due to the complexity of charting needs, there is no single reusable component provided; instead, using Chart.js is recommended. Below are a short instruction and examples on how to get started with Chart.js presented.

Chart.js #

Chart.js is a free JavaScript library for making HTML-based charts. It is one of the simplest visualization libraries for JavaScript, and comes with the many built-in chart types:

• Area Chart
• Bar Chart
• Bubble Chart
• Doughnut and Pie Chart
• Line Chart
• Mixed Chart Types
• Polar Area Chart
• Radar Chart
• Scatter Chart

For more detailed information see the official documentation.

Installation #

To use the package in a project with a bundler, install it via npm:

npm install chart.js

Optionally, you can include Chart.js from a CDN by adding the following to the beginning of your HTML file:

<script src="https://cdn.jsdelivr.net/npm/chart.js"></script>

Usage #

Chart.js renders into an HTML <canvas> element. Add a canvas where you want the chart to appear:

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

Typical Chart Syntax (Bar Chart in this case):

const myChart = new Chart("myChart", {
    type: "bar",
    data: {},
    options: {}
});

The data property contains the labels as well as one or more datasets and the options property configures plugins (e.g., legend, title, tooltip), scales, interaction behavior, and more.

Examples #

In the following, several chart types and features are shown using Chart.js. Note that all values are fictitious and only displayed for visual purposes.

Practical tips #

• Selecting the canvas: new Chart("myChart", ...) works if the element exists. Alternatively, use document.getElementById('myChart') to pass the element directly (as shown in examples).
• Destroy before re-create: If you redraw charts in single-page apps or on data updates, call chart.destroy() before creating a new instance to avoid memory leaks and overlapping canvases.
• Updating data: Update values and call chart.update() to re-render without recreating the chart.
• Color and accessibility: Use high-contrast colors and consider patterns or markers for users with color vision deficiencies.
• Tooltips and formatting: Use tooltip.callbacks and ticks.callback to format values (e.g., currency, percentages).
• Scales: For time-series data, consider the time scale and adapters. For logarithmic data, use the logarithmic scale type.
• Responsive layout: Control chart size via CSS on the canvas or parent container. For fixed height, set height on the canvas or configure maintainAspectRatio in options.
• Bundlers: When importing with npm, you’ll typically do import { Chart, registerables } from 'chart.js'; Chart.register(...registerables); before creating charts.