Quick question when I build a kotlinjs project and...

# javascript

[fkrauthan]

Quick question when I build a kotlinjs project and include a external dependency (for example from NPM) does kotlinjs compiler support tree shaking or will it always include the full external dependency in the final generated code?

[Robert Jaros]

Kotlin compiler doesn't care about external JS dependencies. And it doesn't include any external JS code. The final bundle is generated by webpack.

[turansky]

At current time optimal tree shaking (created by Webpack) blocked by Kotlin/JS:
1. No ES6 modules support => full module imported (not recommended by Google)
2. Redundant package information block tree shaking too
2 steps required for optimal tree shaking:
1. ES6 modules support (partial export/import)
2. Change contract of @JsExport - ignore Kotlin package in JS export by default.

[andylamax]

Are there any plans for kotlin/js to support ES6?

[turansky]

cc @bashor, @anton.bannykh

[bashor]

Yes, we are going to use ES2015 features in near future in the new compiler. Firstly ES2015 classes and modules.

[bashor]

To get updates you can watch (by star or vote) this umbrella issue and/or other issues mentioned there as related.

[fkrauthan]

So if I understand it correctly if kotlinJS starts outputting proper ES6 code webpacks treeshaking should be able todo its work and external dependencies could be reduced as well?

[turansky]

proper ES6 code

ES6 modules with “granular” import

[fkrauthan]

Haha which probably gonna take a long time since all bindings would have to be updated to mark for each reference which file that reference is included in…

[turansky]

No panic! Check required 🙂

[napperley]

Is the ES2015 support likely to appear in a future Kotlin 1.4 release?