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It won't. UglifyJS's dead code elimination is snake oil and mirrors anywhere but in the most trivial of cases.

See:

- https://github.com/webpack/webpack/issues/2867

- https://github.com/webpack/webpack/issues/4784

(Note: webpack doesn't do any dead code elimination, it relies on UglifyJS to do so)

Those are good links to interesting discussions on the topic, I guess UglifyJS is better than nothing although you're right there.

Are you aware of any alternative that can do tree shaking? Reading those issues' comments there is a link to babel-webpack-tree-shaking [1] which seems to do it?

[1] https://github.com/Aladdin-ADD/babel-webpack-tree-shaking

Rollup [1] seems to be pretty good at tree-shaking and apparently babel's babili minifier [2] is better than UglifyJS (but I guess it's too early to tell)

But both come with their own tradeoffs: Rollup is ES6 only and doesn't support certain features from TC39's Stage 3. Babili is very very new :)

[1] https://rollupjs.org

[2] https://github.com/babel/minify

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