As the ECMAScript specification evolves, industrial-scale JavaScript compilers face the challenge of supporting modern language syntax while maintaining compatibility for diverse execution environments. Traditionally, compilers solve this by running transpilation passes in a monolithic pipeline, where the transpilation passes are chosen to execute strictly based on a target language level. This results in significant computational waste, as compilers perform expensive Abstract Syntax Tree (AST) traversals to lower features that may not exist in the actual input source code. We present a compiler improvement that conditionally executes transpiler passes based on accurately tracking and dynamically maintaining the exact set of language features present in the compilation unit throughout the transpilation process. It is implemented in the production Google Closure Compiler. By populating and maintaining a FeatureSet at every JavaScript script-level, it dynamically skips running unnecessary lowering passes. We detail the architectural safeguards—including strategic pass ordering and dynamic validation of the transpiled code for feature-correctness. Evaluation of this improvement on large-scale production monorepos and synthetic benchmarks produced a considerable reduction in compilation time and saved compute and memory usage.

Rishipal is a Senior ML Compiler Engineer at Google. He is a 2016 alumnus of Georgia Tech and has extensive experience optimizing compilers across various domains, including web technologies, computer graphics, machine learning, and artificial intelligence. Prior to his current role, Rishipal was a Senior Software Engineer at Intel, Santa Clara, from 2016 to 2019. There, he focused on optimizing graphics and machine learning workloads for Intel’s GEN Processor Graphics architecture as part of the Intel Graphics Compiler team. From 2019 to 2025, Rishipal was a Senior Software Engineer on Google’s TypeScript/JavaScript compiler team. In this position, he made significant improvements to Google’s JavaScript transpiler and optimizer, redesigned the JavaScript conformance checking infrastructure, and developed numerous compiler-centric tools. He also represented Google as a delegate for the ECMAScript TC39 committee, contributing to the definition of the ECMAScript 2026+ standard language specification. Presently, Rishipal applies his expertise in compiler design to the TPU Compiler, where he explores innovative optimizations for Google’s Tensor Processing Units.