Why Use the JS Dev Environment
Here are the three problems this environment solves.
In this proper code editor, a FileMaker developer can focus her thoughts on the code.
While coding in a code editor, the FileMaker developer can see the results of her work over in the FileMaker web viewer object. After saving the files inside the code editor and pressing the "Load Webviewer" button, the results will show up.
It is so much easier to see the results of the code in another app, and seeing the render update while typing. It's like having a layout mode to the left and a browse mode to the right on your screen. This is how web developers work all the time, and we are able to replicate that using this environment.
Once she's done writing her code, the FileMaker developer can easily deploy the code into the FileMaker file for all people to use. Previously this was a laborious task. With this environment, she is able to deploy and redeploy as often as possible.
Again, web developers are used to this. After I'm finished writing this document, I'll deploy it to the host where it will be available for anyone to read. So too can we do this using this environment.
Just use it!
You can learn all about how this works under the hood, but just know that it works. Write some HTML and some JS, get some data flowing into your widget, and you've got a great widget you can use in one or many projects.