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Creating a Kotlin JavaScript library with the Command Line Compiler

This tutorial walks us through creating a Kotlin JavaScript library using the command line compiler.

Creating a Kotlin/JavaScript library

We will create a simple Kotlin/JavaScript library.

  1. Using our favorite editor, we create a new file called library.kt:

    package org.sample
    fun factorial(n: Int): Long = if (n == 0) 1 else n * factorial(n - 1)
    inline fun IntRange.forOdd(f: (Int) -> Unit) {
        this.forEach { if (it % 2 == 1) f(it) }
  2. Compile the library using the JS compiler

    $ kotlinc-js -output sample-library.js -meta-info library.kt

    The -meta-info option indicates that an additional JS file with binary meta-information about compiled kotlin code will be created.

    If you want to see all available options run

    $ kotlinc-js -help

    After compilation we have two new files:

  3. You can simply distribute two JS files, sample-library.js and sample-library.meta.js. The former file contains translated JavaScript code, the latter file contains some meta-information about Kotlin code, which is needed by compiler.

    Alternatively, you can append the content of sample-library.meta.js to the end of sample-library.js and distribute only the resulting file.

    Also you can create an archive, which can be distributed as a library:

    $ jar cf sample-library.jar *.js

Using a Kotlin/JavaScript library.

Create binom.kt:

import org.sample.factorial
import org.sample.forOdd
fun binom(m: Int, n: Int): Long =
    if (m < n) factorial(n) / factorial(m) / factorial(n-m) else 1
fun oddFactorial(n: Int): Long {
    var result: Long = 1L
    (1..n).forOdd { result = result * it }
    return result

Compile with library:

   $ kotlinc-js -output binom.js -libraries sample-library.meta.js binom.kt

Both files sample-library.js and sample-library.meta.js should be present in the latter case, because translated JavaScript file contains meta-information about inlining, which is needed by compiler.

If you have an archive sample-library.jar, which contains sample-library.js and sample-library.meta.js, you can use the following command

   $ kotlinc-js -output binom.js -libraries sample-library.jar binom.kt