We chose JavaScript/Node because it's the language we knew best, and because we have to write it in the client as we're building a web-based service. No other l

We chose JavaScript/Node because it's the language we knew best, and because we have to write it in the client as we're building a web-based service. No other language offers us that, unless it compiles to JavaScript (eg TypeScript). This grants us a magnitude of benefits, like being able to do server-side rendering and share code between the client and server. It also means we only need to hire people who can write JS, instead of JS and something else. TypeScript, Flow, and ESLint aren't hacks. These are mature tools used by some of the largest, most sophisticated engineering teams in the world.