jsii allows code in any language to naturally interact with JavaScript classes. It is the technology that enables the AWS Cloud Development Kit to deliver polyglot libraries from a single codebase!

A class library written in TypeScript can be used in projects authored in TypeScript or Javascript (as usual), but also in Python, Java, C# (and other languages from the .NET family), ...

NOTE: Due to performance of the hosted Javascript engine and marshaling costs, jsii modules are best suited for development and build tools, as opposed to performance-sensitive or resource-constrained applications.

See Runtime Architecture for more information.

Consider the following TypeScript class:

export class HelloJsii {
  public sayHello(name: string) {
    return `Hello, ${name}!`
  }
}

By compiling our source module using jsii, we can now package it as modules in one of the supported target languages. Each target module has the exact same API as the source. This allows users of that target language to use HelloJsii like any other class:

• In Python:

  hello = HelloJsii()
  hello.say_hello("World"); # => Hello, World!

• In Java

  final HelloJsii hello = new HelloJsii();
  hello.sayHello("World"); // => Hello, World!

• In C#

  var hello = new HelloJsii();
  hello.SayHello("World"); // => Hello, World!

• ... and more to come!

jsii consists of multiple single-purposed programs which can be used to compose various workflows.

We are considering creating an "umbrella entrypoint" to make it easier to consume.

"Community": a community-maintained project, not officially supported by the jsii team.

Let's create our first jsii TypeScript module (actual outputs may slightly differ):

$ mkdir hello-jsii
$ cd hello-jsii
$ npm init -y
Wrote to /tmp/hello-jsii/package.json:

{
  "name": "hello-jsii",
  "version": "1.0.0",
  "description": "",
  "main": "index.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "keywords": [],
  "author": "",
  "license": "ISC"
}
$ npm i --save-dev jsii jsii-pacmak
npm notice created a lockfile as package-lock.json. You should commit this file.
npm WARN [email protected] No description
npm WARN [email protected] No repository field.

+ [email protected]
+ [email protected]
added 65 packages from 54 contributors and audited 191 packages in 7.922s
found 0 vulnerabilities

Edit the package.json file:

/// package.json
{
  // ...
  "main": "lib/index.js",
  "types": "lib/index.d.ts",
  "scripts": {
    "build": "jsii",
    "build:watch": "jsii -w",
    "package": "jsii-pacmak"
  },
  "jsii": {
    "outdir": "dist",
    "targets": {
      "python": {
        "distName": "acme.hello-jsii",
        "module": "acme.hello_jsii"
      },
      "java": {
        "package": "com.acme.hello",
        "maven": {
          "groupId": "com.acme.hello",
          "artifactId": "hello-jsii"
        }
      },
      "dotnet": {
        "namespace": "Acme.HelloNamespace",
        "packageId": "Acme.HelloPackage"
      }
    }
  },
  "author": {
    "name": "John Doe"
  },
  "repository": {
    "url": "https://github.com/acme/hello-jsii.git"
  }
  // ...
}

Read more about what those configuration entries do in the configuration documentation.

Okay, we are ready to write some code. Create a lib/index.ts file:

/// lib/index.ts
export class HelloJsii {
  public sayHello(name: string) {
    return `Hello, ${name}!`;
  }
}

Build your module:

$ npm run build

If build succeeds, you will see the resulting lib/index.js and lib/index.d.ts files were produced, as well as the .jsii file (contents may vary):

/// .jsii
{
  "author": {
    "name": "John Doe",
    "roles": [
      "author"
    ]
  },
  "description": "hello-jsii",
  "homepage": "https://github.com/acme/hello-jsii.git",
  "jsiiVersion": "0.14.3 (build 1b1062d)",
  "license": "ISC",
  "name": "hello-jsii",
  "repository": {
    "type": "git",
    "url": "https://github.com/acme/hello-jsii.git"
  },
  "schema": "jsii/0.10.0",
  "targets": {
    "dotnet": {
      "namespace": "Acme.HelloNamespace",
      "packageId": "Acme.HelloPackage"
    },
    "java": {
      "maven": {
        "artifactId": "hello-jsii",
        "groupId": "com.acme.hello"
      },
      "package": "com.acme.hello"
    },
    "js": {
      "npm": "hello-jsii"
    },
    "python": {
      "distName": "acme.hello-jsii",
      "module": "acme.hello_jsii"
    }
  },
  "types": {
    "hello-jsii.HelloJsii": {
      "assembly": "hello-jsii",
      "fqn": "hello-jsii.HelloJsii",
      "initializer": {},
      "kind": "class",
      "locationInModule": {
        "filename": "lib/index.ts",
        "line": 1
      },
      "methods": [
        {
          "locationInModule": {
            "filename": "lib/index.ts",
            "line": 2
          },
          "name": "sayHello",
          "parameters": [
            {
              "name": "name",
              "type": {
                "primitive": "string"
              }
            }
          ],
          "returns": {
            "type": {
              "primitive": "string"
            }
          }
        }
      ],
      "name": "HelloJsii"
    }
  },
  "version": "1.0.0",
  "fingerprint": "XYWYOiOupH4MmIjFj84wTSRfWqSw8hW37vHkVMO7iuY="
}

This file includes all the information needed in order to package your module into every jsii-supported language. It contains the module metadata from package.json and a full declaration of your module's public API.

Okay, now the magic happens:

$ npm run package

> [email protected] package /Users/rmuller/Development/Demos/hello-jsii
> jsii-pacmak -v

[jsii-pacmak] [INFO] Building hello-jsii (python,java,dotnet,js) into dist
[jsii-pacmak] [INFO] Packaged. java (4.3s) | dotnet (2.0s) | python (0.9s) | npm pack (0.5s) | js (0.0s)

Now, if you check out the contents of dist, you'll find:

dist
├── dotnet
│   ├── Acme.HelloPackage.1.0.0.nupkg
│   └── Acme.HelloPackage.1.0.0.symbols.nupkg
├── java
│   └── com
│       └── acme
│           └── hello
│               └── hello-jsii
│                   ├── 1.0.0
│                   │   ├── hello-jsii-1.0.0-javadoc.jar
│                   │   ├── hello-jsii-1.0.0-javadoc.jar.md5
│                   │   ├── hello-jsii-1.0.0-javadoc.jar.sha1
│                   │   ├── hello-jsii-1.0.0-sources.jar
│                   │   ├── hello-jsii-1.0.0-sources.jar.md5
│                   │   ├── hello-jsii-1.0.0-sources.jar.sha1
│                   │   ├── hello-jsii-1.0.0.jar
│                   │   ├── hello-jsii-1.0.0.jar.md5
│                   │   ├── hello-jsii-1.0.0.jar.sha1
│                   │   ├── hello-jsii-1.0.0.pom
│                   │   ├── hello-jsii-1.0.0.pom.md5
│                   │   └── hello-jsii-1.0.0.pom.sha1
│                   ├── maven-metadata.xml
│                   ├── maven-metadata.xml.md5
│                   └── maven-metadata.xml.sha1
├── js
│   └── [email protected]
└── python
    ├── acme.hello-jsii-1.0.0.tar.gz
    └── acme.hello_jsii-1.0.0-py3-none-any.whl

These files are ready-to-publish artifacts for each target language. You can see the npm tarball under js, the python package under python, the Maven repo under java, etc...

That's it. You are ready to rock!

• TypeScript with some restrictions

• Javascript - generates an NPM package implicitly (no configuration required).
• Python - generates a ready-to-publish PyPI package.
• Java - generates a ready-to-publish Maven package.
• .NET - generates a ready-to-publish NuGet package.

See the configuration documentation for more information on configuring the various targets.

See CONTRIBUTING.

jsii is distributed under the Apache License, Version 2.0.

See LICENSE and NOTICE for more information.