Run JavaScript code asynchronously with simple, idiomatic APIs. Integrates with coroutines, supports bindings, ES modules, and provides robust error handling and type mappings. Ideal for flexible, cross-platform development.
Run your JavaScript code in Kotlin, asynchronously.
This is a QuickJS binding for idiomatic Kotlin, inspired by Cash App's Zipline (previously Duktape Android) but with more flexibility.
There are a few QuickJS wrappers for Android already. Some written in Java are not Kotlin Multiplatform friendly, and some lack updates.
Zipline is great and KMP-friendly, but it focuses on running Kotlin/JS modules. Its API is limited to running arbitrary JavaScript code with platform bindings.
That's why I created this library, with some good features:
In build.gradle.kts:
implementation("io.github.dokar3:quickjs-kt:<VERSION>")
Or in libs.versions.toml:
quickjs-kt = { module = "io.github.dokar3:quickjs-kt", version = "<VERSION>" }
A desktop JVM cannot load the Android native library, so local unit tests need the
-jvm artifact instead:
configurations.matching { it.name.endsWith("UnitTestRuntimeClasspath") }.configureEach {
resolutionStrategy.dependencySubstitution {
substitute(module("io.github.dokar3:quickjs-kt-android"))
.using(module("io.github.dokar3:quickjs-kt-jvm:<VERSION>"))
}
}
Instrumented tests run on a device, they need no substitution.
with DSL (This is recommended if you don't need long-live instances):
coroutineScope.launch {
val result = quickJs {
evaluate<Int>("1 + 2")
}
}
without DSL:
val quickJs = QuickJs.create(Dispatchers.Default)
coroutineScope.launch {
val result = quickJs.evaluate<Int>("1 + 2")
quickJs.close()
}
Evaluate the compiled bytecode:
coroutineScope.launch {
quickJs {
val bytecode = compile("1 + 2")
val result = evaluate<Int>(bytecode)
}
}
With DSL:
quickJs {
define("console") {
function("log") { args ->
println(args.joinToString(" "))
}
}
function("fetch") { args ->
someClient.request(args[0])
}
function<String, String>("greet") { "Hello, $it!" }
evaluate<Any?>(
"""
console.log("Hello from JavaScript!")
fetch("https://www.example.com")
greet("Jack")
""".trimIndent()
)
}
With Reflection (JVM only):
class Console {
fun log(args: Array<Any?>) = TODO()
}
class Http {
fun fetch(url: String) = TODO()
}
quickJs {
define<Console>("console", Console())
define<Http>(, Http())
evaluate<Any?>(
.trimIndent()
)
}
Binding classes need to be added to Android's ProGuard rules files.
-keep class com.example.Console { *; }
-keep class com.example.Http { *; }
This library gives you the ability to define async functions. Within the QuickJs instance, a coroutine scope is created to launch async jobs, a job Dispatcher can also be passed when creating the instance.
evaluate() and quickJs{} are suspend functions, which make your async jobs await in the caller scope. All pending jobs will be canceled when the caller scope is canceled or the instance is closed.
To define async functions, easily call asyncFunction():
quickJs {
define("http") {
asyncFunction("request") {
// Call suspend functions here
}
}
asyncFunction("fetch") {
// Call suspend functions here
}
}
In JavaScript, you can use the top level await to easily get the result:
const resp = await http.request("https://www.example.com");
const next = await fetch("https://www.example.com");
Or use Promise.all() to run your request concurrently!
const responses = await Promise.all([
fetch("https://www.example.com/0"),
fetch("https://www.example.com/1"),
fetch("https://www.example.com/2"),
])
Cancelling the calling coroutine interrupts the evaluation, even if it is busy running JavaScript like an infinite loop:
withTimeout(1000) {
quickJs.evaluate<Unit>("while(true){}")
}
A timeout can also be set on the instance, evaluations running past it will
throw a QuickJsInterruptedException:
quickJs.evaluationTimeoutMillis = 1000
To interrupt manually from anywhere, call interruptEvaluation():
quickJs.interruptEvaluation()
QuickJsInterruptedException extends QuickJsException, so catch it first if you
handle both, otherwise an interrupted evaluation looks like a script error.
ES Modules are supported by passing asModule = true to evaluate() or compile().
Use a ModuleLoader to provide imported modules. It can return source code or cached bytecode:
val sources: Map<String, String> = downloadModuleSources()
val bytecodeCache = mutableMapOf<String, ByteArray>()
val loader = moduleLoader {
normalize { baseName, requestedName ->
resolveModuleName(baseName, requestedName)
}
load { name ->
bytecodeCache[name]
?.let(ModuleContent::Bytecode)
?: sources[name]?.let(ModuleContent::Source)
}
onCompiled { name, bytecode ->
bytecodeCache[name] = bytecode
}
onLoadFailed { name ->
enqueueModuleBytecodeInvalidation(name)
}
}
quickJs(moduleLoader = loader) {
result: ? =
function() { result = (it.first() Number).toInt() }
evaluate<Any?>(
.trimIndent(),
filename = ,
asModule = ,
)
assertEquals(, result)
}
normalize() optionally maps imports to canonical names; otherwise QuickJS uses its default normalization. load() handles static and dynamic imports, onCompiled() receives bytecode for source modules, and onLoadFailed() receives the normalized name when loading fails. All callbacks are synchronous, so keep them fast, avoid blocking persistence, and do not re-enter the same QuickJs instance.
Use resolveModuleGraph() to load and compile the static imports of cached entry bytecode without evaluating it:
quickJs(moduleLoader = loader) {
resolveModuleGraph(cachedEntryBytecode)
evaluate<Any?>(cachedEntryBytecode)
}
QuickJS bytecode is engine-version-specific and must use the same module name. Only load bytecode from a trusted source. Cache storage and invalidation are up to the application; onLoadFailed() can enqueue invalidation of a failed cached module.
When evaluating ES module code, no return values will be captured, you may need a function binding to receive the result.
quickJs {
// ...
var result: Any? = null
function("returns") { result = it.first() }
evaluate<Any?>(
"""
import * as hello from "hello";
// Pass the script result here
returns(hello.greeting());
""".trimIndent(),
asModule = true,
)
assertEquals("Hi from the hello module!", result)
}
Want shorter DSL names?
quickJs {
def("console") {
prop("level") {
getter { "DEBUG" }
}
func("log") { }
}
func("fetch") { "Hello" }
asyncFunc("delay") { delay(1000) }
eval<Any?>("fetch()")
eval<Any?>(compile(code = "fetch()"))
}
Use the DSL aliases then!
-import com.dokar.quickjs.binding.define
-import com.dokar.quickjs.binding.function
-import com.dokar.quickjs.binding.asyncFunction
-import com.dokar.quickjs.evaluate
+import com.dokar.quickjs.alias.def
+import com.dokar.quickjs.alias.func
+import com.dokar.quickjs.alias.asyncFunc
+import com.dokar.quickjs.alias.eval
+import com.dokar.quickjs.alias.prop
For consumer-native bindings, injections, or direct QuickJS operations, use the experimental scoped native context API. The callback runs while the QuickJS instance is exclusively locked. Native pointers must not be retained or used after the callback returns.
@OptIn(ExperimentalQuickJsApi::class)
quickJs.onNativeClose { context ->
NativeBindings.uninstall(context)
}
@OptIn(ExperimentalQuickJsApi::class)
quickJs.withNativeContext { context ->
NativeBindings.install(context)
}
QuickJsNativeContext exposes native addresses on JVM/Android and typed C
pointers on Kotlin/Native. Cleanup callbacks run before the runtime and
context are released, in reverse registration order.
Some built-in types are mapped automatically between C and Kotlin, this table shows how they are mapped.
(1) A Kotlin Unit will be mapped to a JavaScript undefined, conversely, JavaScript undefined won't be mapped to Kotlin Unit.
(2) When converting a JavaScript Number to Kotlin Int, Short, Byte or Float and the value is out of range, it will throw
TypeConverters are used to support mapping non-built-in types. You can implement your own type
converters:
You can also use the converter from quickjs-kt-converter-ktxserialization
and quickjs-kt-convereter-moshi (JVM only).
[!NOTE] Functions with generic <T, R> require exactly 1 parameter on the JS side, it will throw if no parameter is passed or multiple parameters are passed.
Most of functions may throw:
IllegalStateException, if some function was called after calling closeevaluate(), compile(), resolveModuleGraph(), and addModule(bytecode) may throw:
QuickJsException, if a JavaScript error occurred or failed to map a type between JavaScript and KotlinWhen a QuickJsException comes from a JavaScript error, it also tells you where
it was thrown, which is handy for pointing at the offending line:
try {
quickJs.evaluate<Unit>(code, filename = "app.js")
} catch (e: QuickJsException) {
println("${e.fileName}:${e.lineNumber}:${e.columnNumber}")
println(e.stack)
}
Those are all null when the error carries no location, for example when the
JavaScript code threw a plain value like throw 'Bad'.
If you find other suspicious errors, please feel free to open an issue to report
You may need these tools to build and run this project:
Copyright 2024 dokar3
Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at
http:
Unless applicable law agreed to writing, software
distributed under the License distributed an BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express implied.
See the License the specific language governing permissions
limitations under the License.
async and suspended. See #AsyncAndroid, JVM and Kotlin/Native| JavaScript type | Kotlin type |
|---|
| null | null |
| undefined | null (1) |
| boolean | Boolean |
| Number | Long/Int/Short/Byte, Double/Float (2) |
| string | String |
| Array | List<Any?> |
| Set | Set<Any?> |
| Map | Map<Any?, Any?> |
| Error | Error |
| object | JsObject |
| Int8Array | ByteArray |
| UInt8Array | UByteArray |
data class FetchParams(val url: String, val method: String)
// interface JsObjectConverter<T : Any?> : TypeConverter<JsObject, T>
object FetchParamsConverter : JsObjectConverter<FetchParams> {
override val targetType: KType = typeOf<FetchParams>()
override fun convertToTarget(value: JsObject): FetchParams = FetchParams(
url = value["url"] as String,
method = value["method"] as String,
)
override fun convertToSource(value: FetchParams): JsObject =
mapOf("url" to value.url, "method" to value.method).toJsObject()
}
quickJs {
addTypeConverters(FetchParamsConverter)
asyncFunction<FetchParams, String>("fetch") {
// Use the typed fetch params
val (url, method) = it
TODO()
}
val result = evaluate<String>(
"""await fetch({ url: "https://example.com", method: "GET" })"""
)
}
Add the dependency
implementation("io.github.dokar3:quickjs-kt-converter-ktxserialization:<VERSION>")
// Or use the moshi converter
implementation("io.github.dokar3:quickjs-kt-converter-moshi:<VERSION>")
Add the type converters of your classes
import com.dokar.quickjs.conveter.SerializableConverter
// For moshi
import com.dokar.quickjs.conveter.JsonClassConverter
@kotlinx.serialization.Serializable
// For moshi
@com.squareup.moshi.JsonClass(generateAdapter = true)
data class FetchParams(val url: String, val method: String)
quickJs {
addTypeConverters(SerializableConverter<FetchParams>())
// For moshi
addTypeConverters(JsonClassConverter<FetchParams>())
asyncFunction<FetchParams, String>("fetch") {
// Use the typed fetch params
val (url, method) = it
TODO()
}
val result = evaluate<String>(
"""await fetch({ url: "https://example.com", method: "GET" })"""
)
}
js-eval samplejs-eval but it has some Web API polyfills to run the bundled openai-nodeopenai sampleSurfaced from shared tags and platforms — no rankings paid for.