A 'Hello World' program is a rite of passage for a coder, started by Dr. Brian Kernighan, a computing pioneer at Bell Labs.
Code developers have their quirks. Color me shocked.
One of them is to author code that prints the phrase 'Hello World' on a display device. Big whoop, but that often launches a process that can change people's lives. That's what we are doing here. (Changing people's lives, wink).
Hello, DOM
If you examine the original HTML file, you'll notice that there is NOTHING in the div with id="results". When we click the blue button however, something is inserted into the fabric of the page ~ our 'Hello World' message!. That is the magic of JavaScript utilizing the power of the Document Object Model, aka DOM.
The DOM is a digitized structure of an HTML webpage in a browser. It is made up of 'objects' that are arranged in relationship to one another. We can target elements in the DOM (often using their id attribute) using JS and then do tricks with those elements. We can even create 'elements' out of thin air and insert them into our webpage, just as if they had been placed there from the beginning. Study our code carefully to see how this was done.
Pure magic!
View your freshly-rendered source code
in the console panel (Shift-Control-J)
For some real amusement, you can see our original Hello World app written in PHP!
While you're at it, check this out: In 2025 we used Copilot to generate a whimsical 'Hello World' program in 3 different languages