I just created a kotlin multiplatform library for android, ios and Javascript which uses the Ktor client for all networking. These are my dependencies for the javascript library

// MPP - JS & common dependencies

    sourceSets["commonMain"].dependencies {
        implementation(kotlin("stdlib-common", Versions.KOTLIN))
        implementation(Deps.Ktor.COMMON_CORE)
        implementation(Deps.Ktor.COMMON_JSON)
        implementation(Deps.Coroutines.COMMON)
        implementation(Deps.MP_SETTINGS)
        implementation(Deps.Ktor.COMMON_SERIALIZER)
        implementation(Deps.Serialization.COMMON)
        implementation(Deps.Stately.COMMON)
        implementation(Deps.Stately.CONCURRENCY)
    }    

    sourceSets["jsMain"].dependencies {
        implementation((kotlin("stdlib-js", Versions.KOTLIN)))
        implementation(Deps.Ktor.JS_CORE)
        implementation(Deps.Ktor.JS_JSON)
        implementation(Deps.Coroutines.JS)
        implementation(Deps.Ktor.JS_SERIALIZER)
        implementation(Deps.Serialization.JS)
    }

My goal is to write the repository layer as a library for the three platforms which can use it to request proprietary data, similar to Firebase Realtime database. But when I import the JS library into the Jetbrains starter React app my javascript binary is 27MiB for dev and 1MiB for prod distributions. Should I expect ktor & coroutines JS libraries to be that heavy for a JS library? Or am I doing something wrong?

You can check your

build/js/packages/[project]/kotlin-dce

directory - there you will find all kotlin js files used by your project (already processed by DCE). You can compare sizes of different libs.

thanks again

Those files are used by webpack, combined with npm JS dependencies, bundled and once again minified with Terser plugin. Your ~1MB is the result.

That’s unfortunate. It would be really nice to use coroutines as a unified architecture for asynchronous programming in common code. I guess I might just have to figure out a way to abstract it away for JS

My largest Kotlin/JS project is 3,2MB bundle size. And it's usable 😉 Fortunately after gzip it's only ~600KB 😉

Kotlin 1.4 is said to dramatically decrease JS bundle size. You could try the M3 release.

Unfortunately, I have deps that are not 1.4 M3 compatible. But good to know, thank you

This image was shared at the 1.4 keynote to get an impression how big the improvement is.

From my tests the improvement is not as big as shown on slides (I'v got only about 30% reduction of the bundle size). It probably very much depends on your libraries.