The language itself is (usually) the easy part. If you need a senior frontend engineer, JavaScript knowledge is table stakes. You need someone who can collabo

The language itself is (usually) the easy part. If you need a senior frontend engineer, JavaScript knowledge is table stakes. You need someone who can collaborate with product and design, and work with the engineering team on platform and implementation decisions. If you need a senior backend engineer you need someone who's really familiar with server side APIs, database behavior, and data model patterns who can advise the product team on what is reasonably possible and what is practically impossible. And these are just the baselines; we're not talking about emergencies, outages, modern software development (continuous integration, testing, deployment, etc.), or "intangibles" like attitude. Basically that's why hiring engineers is so hard. There are 1000 variables and really they're all important.