JavaScriptCore is an optimizing virtual machine for JavaScript used on every iPhone and macOS device in the world. We will explore the intricacies of the JavaScriptCore compiler infrastructure in detail. JavaScriptCore is not a single compiler but a family of compilers: it comprises three compilers for JavaScript, two for WebAssembly, one for regular expressions, one for cascading style sheets (CSS), and one for the document object model (DOM). This talk will explain the method to the madness, the strategy and motivation for having an army of compilers. Then we conduct a deep dive into our “FTL”, the high-throughput just-in-time compiler for JavaScript.

I work on compilers and language runtime systems at Apple. Most of my work there involves the WebKit open source project.