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50 lines
2.5 KiB
Markdown
50 lines
2.5 KiB
Markdown
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# Optimizing for Size with `wasm-bindgen`
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The Rust and WebAssembly Working Group's [Game of Life tutorial][gol] has an
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excellent section on [shrinking wasm code size][size], but there's a few
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`wasm-bindgen`-specific items to mention as well!
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First and foremost, `wasm-bindgen` is designed to be lightweight and a "pay only
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for what you use" mentality. If you suspect that `wasm-bindgen` is bloating your
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program that is a bug and we'd like to know about it! Please feel free to [file
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an issue][issue], even if it's a question!
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### What to profile
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With `wasm-bindgen` there's a few different files to be measuring the size of.
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The first of which is the output of the compiler itself, typically at
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`target/wasm32-unknown-unknown/release/foo.wasm`. **This file is not optimized
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for size and you should not measure it.** The output of the compiler when
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linking with `wasm-bindgen` is by design larger than it needs to be, the
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`wasm-bindgen` CLI tool will automatically strip all unneeded functionality out
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of the binary.
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This leaves us with two primary generated files to measure the size of:
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* **Generated wasm** - after running the `wasm-bindgen` CLI tool you'll get a
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file in `--out-dir` that looks like `foo_bg.wasm`. This file is the final
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fully-finished artifact from `wasm-bindgen`, and it reflects the size of the
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app you'll be publishing. All the optimizations [mentioned in the code size
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tutorial][size] will help reduce the size of this binary, so feel free to go
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crazy!
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* **Generated JS** - the other file after running `wasm-bindgen` is a `foo.js`
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file which is what's actually imported by other JS code. This file is already
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generated to be as small as possible (not including unneeded functionality).
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The JS, however, is not uglified or minified, but rather still human readable
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and debuggable. It's expected that you'll run an uglifier or bundler of the JS
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output to minimize it further in your application. If you spot a way we could
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reduce the output JS size further (or make it more amenable to bundler
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minification), please let us know!
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### Example
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As an example, the `wasm-bindgen` repository [contains an example][example]
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about generating small wasm binaries and shows off how to generate a small wasm
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file for adding two numbers.
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[gol]: https://rustwasm.github.io/book/game-of-life/introduction.html
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[size]: https://rustwasm.github.io/book/game-of-life/code-size.html
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[issue]: https://github.com/rustwasm/wasm-bindgen/issues/new
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[example]: https://rustwasm.github.io/wasm-bindgen/examples/add.html
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