QuickJS - KT

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.

Another QuickJS wrapper?

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:

• Simple and idiomatic Kotlin APIs, it's easy to define binding and evaluate arbitrary code
• Highly integrated with Kotlin Coroutines, it is async and suspended. See #Async
• Kotlin Multiplatform targets, including Android, JVM and Kotlin/Native
• The latest version of QuickJS

Usages

Installation

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>" }

Evaluate

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)
    }
}

Bindings

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", Http())

    evaluate<Any?>(
        """
        console.log("Hello from JavaScript!")
        http.fetch("https://www.example.com")
        """.trimIndent()
    )
}

Binding classes need to be added to Android's ProGuard rules files.

-keep class com.example.Console { *; }
-keep class com.example.Http { *; }

Async

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"),
])

Modules

ES Modules are supported when evaluate() or compile() has the parameter asModule = true.

quickJs {
    // ...
    evaluate<String>(
        """
            import * as hello from "hello";
            // Use hello
        """.trimIndent(),
        asModule = true,
    )
}

Modules can be added using addModule() functions, both code and QuickJS bytecode are supported.

quickJs {
    val helloModuleCode = """
        export function greeting() {
            return "Hi from the hello module!";
        }
    """.trimIndent()
    addModule(name = "hello", code = helloModuleCode)
    // OR
    val bytecode = compile(
        code = helloModuleCode,
        filename = "hello",
        asModule = true,
    )
    addModule(bytecode)
    // ...
}

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)
}

Alias

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

Type mappings

Some built-in types are mapped automatically between C and Kotlin, this table shows how they are mapped.

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

(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

Custom types

TypeConverters are used to support mapping non-built-in types. You can implement your own type converters:

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" })"""
    )
}

You can also use the converter from quickjs-kt-converter-ktxserialization and quickjs-kt-convereter-moshi (JVM only).

1. 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>")

2. 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" })"""
       )
   }

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.

Error handling

Most of functions may throw:

• IllegalStateException, if some function was called after calling close

evaluate() and compile() may throw:

• QuickJsException, if a JavaScript error occurred or failed to map a type between JavaScript and Kotlin
• Other exceptions, if they were occurred in the Kotlin binding

If you find other suspicious errors, please feel free to open an issue to report

Samples

• js-eval: A GUI Compose Multiplatform app to evaluate JS, some minimal JS snippets are builtin
• openai: Like js-eval but it has some Web API polyfills to run the bundled openai-node
• repl: Simple Multiplatform REPL command line tool using clikt

Development

You may need these tools to build and run this project:

• Java JDK, both Windows, macOS, and Linux JDKs are required if you do a cross-compiling
• Android SDK and NDK
• CMake The build system
• Ninja The build generator for CMake
• Zig For cross-compiling the JNI libraries

License

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://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.