Index operator []

This article shows usage of [] operator for arrays and collections. In Javonet, every array or collection from called technology is treated as a reference.

Javonet allows you to reference and use modules or packages written in (Java/Kotlin/Groovy/Clojure, C#/VB.NET, Ruby, Perl, Python, JavaScript/TypeScript) like they were created in your technology. If have not yet created your first project check Javonet overview and quick start guides for your technology.

With Javonet you can interact with arrays from NodeJs package like they were available in C++ but invocation must be performed through Javonet SDK API.

Custom NodeJs package with arrays handling

With Javonet it is possible to reference any custom NodeJs package and interact with arrays declared on types defined within that module almost the same as with any other C++ library.

Snippet below represents the sample code from NodeJs package that has methods which return or process the arrays:

get1DArray() {
	return ["one", "two", "three", "four", "five"]

get2DArray() {
	return [["S00", "S01"], ["S10", "S11"]]
addArrayElementsAndMultiply(myArray, myValue) {
	return myArray.reduce((accumulator, currentValue) => accumulator + currentValue) * myValue

Each array or collection from NodeJs package returns as InvocationContext which contains reference to the target data. Javonet SDK implements [] operator on InvocationContext to interact with complex data objects in C++:

Get element from NodeJs package in C++

// use Activate only once in your app

// create called runtime context
auto calledRuntime = Javonet::InMemory()->Nodejs();

// set up variables
auto libraryPath = resourcesDirectory + "/TestClass.js";
auto className = "TestClass";

// load custom library

// get type from the runtime
auto calledRuntimeType = calledRuntime->GetType(className)->Execute();

// create type's instance
auto instance = calledRuntimeType->CreateInstance()->Execute();

// invoke instance's method
auto arrayReference = instance->InvokeInstanceMethod("get1DArray")->Execute();

// get index from array
auto response = (*arrayReference)[2]->Execute();

// get value from response
auto result = std::any_cast<std::string>(response->GetValue());

// write result to console
std::cout << result << std::endl;

In the snippet above, get1DArray method is used to get reference to 1D array from NodeJs package. Operator [] is used to get element from the array.

Set element from NodeJs package in C++

This snippet doesn't support selected combination of technologies.

In the snippet above, get1DArray method is used to get reference to 1D array from NodeJs package. Operator [] is used to set element of the 1D array.

The same operation can be performed remotely by just changing the new Runtime Context invocation from in memory to tcp that will create and interact with your NodeJs package objects on any remote node, container or service that hosts Javonet Code Gateway. This way you can preserve the same logic in your application and instantly switch between monolithic and microservices architecture without the need to implement the integration layer based on web services or other remote invocation methods.

Read more about use cases and software architecture scenarios where Javonet runtime bridging technology can support your development process.