Downloading and processing OSM XML are some of the slowest tasks in the iD editor. As a user navigates around the map, this activity can block other work, causing delayed rendering and unresponsiveness. However, OSM XML files follow a well-defined format that can be easily parsed, and modern browsers are able to execute tasks asynchronously in multiple threads using a feature called web workers.

This talk showcases several techniques for improving the performance of downloading and parsing data from the OSM API. We’ll do a quick overview of how this faster parser works, discuss performance tricks used, and evaluate the resulting speed and size benefits of the new parser.