We recently shipped a new for Vercel Functions to improve startup times.Rust-based core Today, we are announcing a new experimental feature to further reduce startup latency for large applications, resulting in up to .27% faster cold starts One of the slowest parts of a cold start is loading and compiling the JavaScript source code. Before executing the code, it needs to be parsed and compiled into , which is then directly executed by the V8 virtual machine or compiled into machine code by V8's just-in-time compiler (JIT).bytecode This conversion to bytecode must happen when a JavaScript file is executed for the first time, but it introduces latency.

What if we could cache this step and re-use it later on subsequent cold starts? That's exactly how bytecode caching works. The first execution will produce a bytecode cache, and successive executions and cold starts will re-use and optimize the cache. This can improve the cold start duration by transparently eliminating the compilation step. We initially tested with three different Next.js applications which each load a different amount of JavaScript. Each application would get a cold start every 15 minutes. We compared the startup…