My students Niko Heiskanen and SharkTal wrote a book shop, hlgbooks.com
Buy Niko's booklet "Paypal Integration", 1 EUR. The shop is more beta than the greek letter β, but you can buy from their website if you register first.
And yes, you can have the source code.
You can now write scripts in plain JavaScript. Jquery is mostly not needed for compatiblity.
In 2021, Microsoft desktop and server Windowses only support Internet Explorer 11 or later (Edge). This removes the need for most compatibility hacks. Firefox and Chrome have followed JavaScript standards mostly from the start.
$("h1").text("Goodbye jQuery, my favourite JS library!")
document.querySelector("h1").innerHTML = "Hello, vanilla JavaScript!"
Graph line plots with plotly.js. Plotly is Free software under the MIT license.
Plotly works even if you miss a couple of data points. For example, if you have temperature for all days but Tuesday.