Back in 2012, Mozilla launched Thimble, an online code editor for teaching the basics of HTML, CSS and JavaScript. Over time, though, things got pretty quiet around the project as other browser ...

The project consists of roughly 40,000 lines of HTML radio buttons and labels, combined with fewer than 500 lines of CSS where the real work is done.

One handy component is a timer for executing code at intervals—e.g., for polling a data source for updates. You can also hand-roll your own HTML and custom components.

Code commonly flows downstream, from an open-source project into an organization’s own products. Upstreaming is the process of reversing that flow—contributing code back to an open-source project.