A JavaScript engine for Kotlin Multiplatform, built on the interpreter from Mozilla Rhino. It runs the same script the same way on every target.

Documentation · Getting started · Binding host objects · Differences from a browser · API reference

KiteJs { instructionBudget = 5_000_000 }.use { js ->
    js.global.function<Double, Double, Double>("hypot") { a, b -> hypot(a, b) }
    js.global.obj("document") {
        property("title", "Untitled")
        getter("readyState") { "complete" }
    }
    println(js.evaluate("document.title + ':' + hypot(3, 4)").asString())
}
// Untitled:5

Runs ES5.1 and most of ES2015 and later: let and const, arrow functions, template literals, destructuring, Symbol, Map, Set, WeakMap, WeakSet, generators, Promise, Proxy, Reflect, BigInt, typed arrays, optional chaining, and the full regular expression syntax including named groups and lookbehind. It does not run classes, modules or async/await.

The engine is common Kotlin. There is no platform engine underneath, no native library to ship, and no code generation at runtime. The parser, the regular expression engine, the date arithmetic, the number formatting and the number parsing are all computed inside the engine, so the same script gives the same answer everywhere.

Binding your own functions and objects uses lambdas and property references, not reflection, so it behaves identically on every target too.

JVM (bytecode 11), Android, iOS, macOS, JavaScript, WebAssembly, Linux (x64 and arm64) and Windows.

KiteJS is on Maven Central:

// build.gradle.kts
commonMain.dependencies {
    implementation("io.github.yuroyami:kitejs:0.2.0")
    implementation("io.github.yuroyami:kitejs-coroutines:0.2.0")  // optional
}

The second artifact puts the engine behind suspending functions: awaiting a promise, handing a Deferred to a script, host functions that suspend, and cancellation that stops a running script.

Every script runs through upstream Rhino as well, and the two answers have to match. On the last full test262 run, 52,802 cases went through both engines and none of them disagreed. The same 52,802 cases then run on JavaScript, WebAssembly, iOS and macOS against the outcomes the JVM recorded, so no target can quietly behave differently.

MPL-2.0, because KiteJS is a derivative of Mozilla Rhino. See LICENSE and NOTICE.