In this map, the user is prompted for a State abbreviation. The original layer service is then queried for all the counties in that state and saves the results to an array of graphics. The code then uses those graphics to display a new FeatureLayer with a renderer that shades the county polygons according to the 2020 Vote Margin value (calculated from existing fields containing the vote percentage for each political party). Upon loading the state results, the view zooms to that state. The user can click on the individual counties to bring up popups that give individual county details.
I found this assignment a great deal harder than the previous assignments. I struggled to integrate the code that defined the ClassBreaksRender into the query/selection code. I knew I couldn't add a renderer to a GraphicsLayer, but I didn't know how otherwise to capture the results of a query. Professor Detwiler pointed me to an example in Lesson 8 (Clickable Sidebar List) that added an array of Graphic objects to a FeatureLayer. At first, I found the code hard to read (I haven't done Lesson 8 yet) but once I figured out what parts of the code belonged to each desired action, it was easier to decide what pieces of the code I needed. The second problem that I encountered was getting the Arcade expression to work so the renderer would work. It turns out that I needed to specify the fields I wanted back from the query. I thought all the fields came back by default. Once all the correct fields were retrieved, the Arcade expression and the renderer worked.
Through this assignment, I learned how to work with when/then functions and promises as well as queries. I also learned to better understand the different ways of using properties outside of creating a "new" instance, like working with the view to have it zoom to the selection. I spent a lot of time looking up things in the API Reference and looking at code samples that did similar things in different ways to better understand how the API and JavaScript code works. My increased ability to read and manipulate code will definitely help me as I do more JavaScript programming in the future.