Learning Journal — 2025-10-06: WebAssembly History & Concepts

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Overview

I spent roughly 2 hours understanding how webassembly appeared. Descovered emscripten and asm.js. Interesting stuff. Helped me understand why webassembly is the way it is. I feel like I spent some time jumping between pages, sometimes losing focus, but overall I got a bit clearer picture.

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Key Takeaways

1. Emscripten

   • At first compiles C/C++ to JS was original idea
   • Dude that worked in Mozilla understood that this compilation produced some parts that were identical to after parsing JS code it was C/C++ to JS, after that he asked to make C/C++ to asm.js which is a subset of JS that is easier to optimize

   • When they got approval to make their asm.js on all browsers, they decided to really optimize it and make it a binary format which is WebAssembly

   • Funny note: Emscripten name is a reference to Simpsons episode, where they used embiggen word which is a made up word

2. asm.js

   • Basically a subset of JS optimized for performance. Mozilla created it to run compiled C/C++ code on browsers.
   • Limitation: still parsed as JS → startup slower, more memory overhead.

3. WebAssembly

   • Binary format, sandboxed, runs in browsers.
   • I still don’t fully get memory management between Wasm and JS — will test later.
   • Its interesting to me that maybe its easier to debug asm.js than webassembly, because its still JS after all, and then just recompile to Wasm and run it

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Background & References

• why web assembly is fast
• nice blog, BUT its old and it feels like that people who wrote it didn’t know much about asm.js or emscripten
• REALLY FUCKING NICE ARTICLE

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Relevance & Connections

• Shows why performance-oriented languages can exist in browsers.
• I don’t see strong parallels with earlier topics yet, but I can imagine future Rust → WebAssembly exercises.
• Might relate to future projects: WASI, server-side Wasm, maybe WebGPU integration.

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Confusions & Questions

• How exactly does the browser execute Wasm? Is it JIT or AOT compiled?
• How even browser execute JS?
• Memory: is it shared with JS or copied?
• Debugging: can i debug wasm through debugging it in asm.js and then recompiling to wasm?
• Security: no fucking clue yet.

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Action Plan

1. Review asm.js examples to understand translation pipeline.
2. Track all questions above and see what resources answer them.

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Reflections

• Writing this journal helps me consolidate thoughts and actually think after I learnt something.

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Raw Notes

didn’t do this time, need to do next time

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Summary

No summary