PerfanalyticsJS is a lightweight (it's only 2.79KB, wow!), zero-dependicies, client-side library written in pure JavaScript and bundled with Parsec which collects some performance related key metrics from your web application and sends it to your API you decide.
You can see which metrics have been collected on your browser's console!
Import the minified JavaScript library into your HTML as script like below and that's all! The library will take care of the rest. Your "index.html" is recommended if you want to access metrics on all pages.
<script src="https://apps.erbilnas.com/lib/perfanalytics.js"></script>