Chart.js can be included in several different ways:
Run the following command on your NPM project directory
npm install chart.js --save
Include a script tag in your HTML linking to the chart.js CDN
Latest version can be found at cdnjs.com/libraries/Chart.js.
A local copy can also be hosted on your server. You can get the lasted version from their GitHub.
For more information about getting chart.js installed see www.chartjs.org/docs/.