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deepmind.google·6d ago
AI Engineering
Hacker News·May 20·5 min read
Saying Goodbye to Asm.js
TL;DR
Asm.js, a subset of JavaScript designed to run compiled C/C++ code in browsers at near-native speed, is being phased out. WebAssembly (WASM), a lower-level bytecode format, replaced it by offering better performance, smaller file sizes, and broader language support.
✦ Why It Matters
Engineers maintaining legacy Asm.js codebases should plan migration to WebAssembly to ensure future browser compatibility and performance.
Key Takeaways
- Migrate existing Asm.js codebases to WebAssembly for better performance and smaller binaries.
- Use Emscripten with WebAssembly output target instead of Asm.js for new C/C++ to web projects.
- Expect reduced vendor optimization effort for Asm.js; prioritize WebAssembly for long-term support.
- Plan deprecation timelines for Asm.js dependencies in production systems before browser support erodes.
Full Summary
Asm.js emerged as a bridge technology allowing developers to compile native code (written in C or C++) into a restricted JavaScript subset that browsers could optimize aggressively. It used type annotations and strict syntax rules to signal to JavaScript engines which code paths could be compiled to machine code ahead of time.
However, WebAssembly—a standardized binary intermediate representation—was designed from the ground up to solve the same problem more elegantly, with better performance characteristics, smaller payload sizes, and clearer semantics. As WebAssembly gained browser support and matured, toolchains like Emscripten shifted their default output from Asm.js to WebAssembly.
The transition reflects a natural evolution: Asm.js was a pragmatic workaround within JavaScript's constraints, while WebAssembly is a purpose-built platform feature. Engineers maintaining legacy Asm.js codebases should plan migration strategies to WebAssembly to benefit from ongoing optimization and vendor support.