https://fullstackopen.com/en/part0/fundamentals_of_web_apps

Really fascinating. I can see, literally as a timeline, the timeline of the requests and responses sent.

And, for each element, I can see what data went into the request - in the header, the body, and what files were part of the response. I can see the HTML that was part of the response!

I notice that images, then CSS came back later. I wonder why.

“In traditional web applications, the browser is "dumb". It only fetches HTML data from the server, and all application logic is on the server. A server can be created using Java Spring , Python Flask or Ruby on Rails to name just a few examples.”

• All application logic is on the server. Server decides what information to send to the client. Seems fine so far.

Notes site and how JS works in concert with HTML/CSS

What happens is the browser goes down line by line the HTML file (notes)

• ? Wha

and once it gets to the <script> tag it loads the javascript file.

• ? Does this happen in parallel with loading the rest of the HTML file ?
• Aha, I notice that it’s in the header tag. So that does necessarily happen first (?)
• ChatGPT: Yes, if it’s in the header, it’ll block parsing of the rest of the HTML until the script is fetched and executed.
• Unless, there’s an async attribute - it’ll be fetched in parallel to parsing and executed immediately after (then pausing the HTML parse until it’s done executing?)
• If there’s a **defer attribute, then it’ll fetch in parallel but pause executing until the HTML has been parsed.

The javascript file essentially determines two things - what happens when someone adds a new note, and loads the rest of the “notes” data content in the HTML page.

• ? When does this happen, in the code? And what is the purpose of the xhttp.open snippet? I’m assuming that’s actually pulling the data from the json file to display. But then how does it know to load the data into the div called “notes” if that pointer seems to be tucked inside the onreadystatechange function? When is that called?