Remember our "Simple Liker" program. In it we saw that front end web programming is using three "pillars" working together:

• ☑ Manipulating the DOM
• Recognizing JavaScript events
• Communicate with the server

This whole unit has been about gaining the skills required to Manipulate the DOM. Since you can now update web pages using JavaScript, you can communicate things to users like "You've liked this message" by changing the appearance of the web page they're looking at.

But...obviously most people don't interact with web pages by opening up the Chrome DevTools console and writing JavaScript commands. If we could tell the web page to do that work when some event happens (clicking an image, double clicking inside a square, etc.) we'd be closer to the web experiences that we're already familiar with.

The important part is that you've mastered the first pillar. Two more down and you're going to be building the rich web applications of your dreams!