Browser Syntax Evolution and Support

This feature thread tracks the evolution of how GitHub manages browser support and leverages modern JavaScript syntax for performance improvements. Initially, the focus was on shipping native ES2019 code and understanding browser usage patterns. This post details the plan to serve JavaScript using ECMAScript 2020 syntax (optional chaining, nullish coalescing) for a 10kb reduction, and introduces the open-sourced browser support library. It also provides detailed data on customer browser usage, informing decisions on testing, static analysis, and feature shipping.