A web application is a series of interactive web pages put together and accessed through your browser.
A web page is a group of files that you download from a server
Some websites look the same for everyone, but dynamic sites like Twitter change their content under different circumstances
Web apps like Google Drive are a series of dynamic web pages, usually behind a login
Any software you use on the internet is probably a web app, and almost every application you use follows the same general pattern. So read this!
(I didn’t understand what a web app really was until years after I learned how to code.)
The key to understanding web applications is understanding websites, because apps are just big, self contained sites. And contrary to popular belief, a website is not actual magic.
To get the most out of this post, you’ll want to understand the basics of cloud (what web servers are), as well as the frontend / backend distinction and what’s powering our apps.
When you’re loading a site, you’re actually downloading files from a web server in the cloud. That’s it! The URL in your browser tells the web server which files to send you, and then your browser displays them to you. There are 3 basic types of these files that create what you see on your screen:
HTML: the text and structure of the elements on the page (a header, a paragraph, a table)
CSS: the styling of the words and structures that you defined in your HTML
Contrary to the authoritative tone of this piece of writing, you don’t need to just take my word for any of this. Load a website on your computer (this won’t work on your phone) and save it (File → Save Page As). Head over to your downloads folder (or wherever you saved it) and open the file, and you should see something pretty close to what you’d get if you’d put in the URL. Even if you disconnect from the internet!
When you navigate around a site and click on to a different page, you’re loading a different file (that’s why the URL changes!). A modern website is just a collection of these different files, connected to each other through links (embedded in buttons, arrows, you name it), being sent to your computer whenever you request them. Where things get complicated is how these files get built.
A lot of websites are pretty much the same for everyone who loads them: the front page of the New York Times looks pretty standard, for example. But when you load Twitter, your feed is completely different from what someone else might see on their account. Plus, new tweets seem to show up all the time, without you reloading the page. How is all of that happening?
Websites can load and display content dynamically. Twitter doesn’t send the same files to everyone: they customize what they send you based on who you’re logged in as, who you follow, what words you’ve muted, and other stuff like that. Here’s what’s happening behind the scenes:
You tell the Twitter web server to send you the files for your homepage by putting twitter.com in your browser
Twitter checks who you are – you’re logged in as yourself (nice), with a username
Twitter goes to their database and generates a feed of tweets based on your information
Twitter puts that content in the HTML file, and sends it over to your computer
(To get into the nitty gritty, a bunch of times they’ll send you the files and then add the dynamic content, but that’s for another time)
On most web pages, some content is static and some is dynamic. Think about your Twitter homepage:
A lot of things here don’t change much. The order and the text of the tabs on the left, the logo, the search bar – all of this is the same for everyone. But what shows up in the feed, the little picture of me next to “profile” on the left, and the trending tweets on the right – those are all dynamic. If I had to guess, this is what the Twitter page looks like before the dynamic content gets put in:
Once you log in, Twitter adds your profile photo (they stored it in their database) to the two little gray circles, and populates your feed with the right tweets and trending topics based on what they think you’ll want.
That’s all a web app really is: it’s a series of dynamic web pages. Every piece of software you use follows this paradigm. Let’s take a look at a great example (if I might say so myself) – Google Drive – and walk through what happens when you’re forced to use it under the guise of productivity.
If you haven’t logged in in a while or your preference is to require credentials on every page load, Google Drive will prompt you for your login information. When you set up your account, you chose a username and password; Google stored that information in a database. As you click “login” Google takes the username and password you supplied, and checks it against what they have in their database: if it matches, they let you in.
Everyone’s Google Drive homepage looks different, because like Twitter, almost the entire page is dynamic. Now that you’ve logged in and Google knows who you are, they head into their database and find all of the content (Google Docs, Sheets, and Slides) that you’ve created in the past. They then format that content and slide it into the HTML that shows up in your browser.
Without the dynamic content served from the backend, the page would probably look something like this:
A spreadsheet in Google Sheets is just a bunch of data, and Google is storing and retrieving all of that data constantly. When you create a new Sheet, Google records that in their database. When you edit a cell, create a formula, or create a new sheet, Google records that too. All of the information sits in Google’s servers, and is sent and displayed to your computer; which is why you can access this from any other computer too (cloud!).
There’s a lot to explore around the details of how web apps get built and served, like client side rendering (React, Angular, Vue), HTTP, caching, CDNs, and lots of other stuff. Check out the links for other Technically posts on these topics.
“I like the Desktop version of Excel better. The cloud web app is kind of janky.”
Excel has a web app that works in the cloud, but the version that runs on my laptop is easier to use and more reliable.
“The outage brought down our web app, so we got paged.”
Our cloud provider had a service outage, so our servers weren’t working: they weren’t able to send users the files they needed, so our app went down.
“We started using React a few months ago for our web app”
We’ve been using the React framework (ooh! aah!) to build our web apps and render dynamic content to our users.
HTML / CSS / JS
Rendering dynamic content to your users can happen on the server side or on the client side, and the latter has been getting a lot of love through React and Vue