Yes good luck shipping that main.rs to a web browser.
The problem that Webpack solves is performance optimization in addition to what Rust offers:
- writing in a higher-level language: "write modern code and ship to IE 5" is the same as "write in Rust and ship to x64"
- take a bunch of files and make 1 or 2 out of it.
Nobody stops you from loading jQuery and 3 plugins in a script tag and call it a day. Webpack exists because jQuery and 3 plugins can't deliver the same results nowadays.
Also, do you want to improve your code with types and linting? Do that without Webpack, it's not going to be much more efficient.
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In short, Webpack and Babel basically match the Rust compiler in functionality. If you don't use them, your web app’s code will be harder to manage, not easier. That's all.