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jsii

Build Status

jsii allows code in any language to naturally interact with JavaScript classes.

For example, 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.

NOTE: Due to performance of the hosted JavaScript engine and marshaling costs, jsii modules are likely to be used for development and build tools, as oppose to performance-sensitive runtime behavior.

From Java:

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

From .NET:

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

From Python (WIP):

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

From Ruby (WIP):

hello = HelloJsii.new
hello.say_hello 'World' # => Hello, World!

Here's how it works.

Getting Started

Let's create our first jsii TypeScript module!

$ npm init -y
$ npm i --save-dev jsii jsii-pacmak

Edit your package.json:

{
  // ...

  "main": "lib/index.js",
  "types": "lib/index.d.ts",
  "scripts": {
    "build": "jsii",
    "watch": "jsii -w",
    "package": "jsii-pacmak -v"
  },
  "jsii": {
    "outdir": "dist",
    "targets": {
      "java": {
        "package": "com.acme.hello",
        "maven": {
          "groupId": "com.acme.hello",
          "artifactId": "hello-jsii"
        }
      },
      "dotnet": {
        "namespace": "Acme.HelloNamespace",
        "packageId": "Acme.HelloPackage"
      },
      "sphinx": { }
    }
  }
}

So, what's going on here?

  • The jsii section in your package.json is the jsii configuration for your module. It tells jsii which target languages to package, and includes additional required information for the jsii packager.
  • npm run build uses jsii to compile your code. It invokes the TypeScript compiler (tsc) and will compile your .ts files into .js files.
  • npm run watch will invoke tsc -w which will monitor your filesystem for changes and recompile your .ts files to .js (note that jsii errors will not be reported in this mode)
  • npm run package invokes jsii-pacmak, which is the jsii packager. It will generate and compile your package to all target languages. The output packages will be emitted to outdir (in the above case dist).
  • Other required package.json fields: license, main, types.

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

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

Build your module:

$ npm run build

If build succeeds, you will see the resulting .js file (lib/index.js) produced by the TypeScript compiler.

You should also see a .jsii file in the root:

{
  "fingerprint": "HB39Oy4HWtsnwdRnAFYl+qlmy8Z2tmaGM2KDDe9/hHo=",
  "license": "Apache-2.0",
  "name": "hello-jsii",
  "schema": "jsii/1.0",
  "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"
    }
  },
  "types": {
    "hello-jsii.HelloJsii": {
      "assembly": "hello-jsii",
      "fqn": "hello-jsii.HelloJsii",
      "initializer": {
        "initializer": true
      },
      "kind": "class",
      "methods": [
        {
          "name": "sayHello",
          "parameters": [
            {
              "name": "name",
              "type": {
                "primitive": "string"
              }
            }
          ],
          "returns": {
            "primitive": "string"
          }
        }
      ],
      "name": "HelloJsii",
      "namespace": "hello-jsii"
    }
  },
  "version": "1.0.0"
}

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
[jsii-pacmak] [INFO] Building hello-jsii (java,dotnet,sphinx,npm) into dist

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

├── dotnet
│   └── Acme.Hello.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
│   └── hello-jsii@1.0.0.jsii.tgz
└── sphinx
    └── hello-jsii.rst

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

That's it. You are ready to rock!

Features

Language features

  • Classes
  • Inheritance
  • Constructors
  • Methods
  • Properties
  • Abstract Members
  • Virtual Overrides
  • Async Methods
  • Variadic Arguments
  • Static Methods and Properties
  • Static Constants
  • Abstract Classes
  • Interfaces
  • Enums
  • Primitive Types: string, number, boolean, date, json, any
  • Collection Types: arrays, maps
  • Union Types (limited support)
  • Module Dependencies
  • Data Interfaces

Source Languages

  • TypeScript

Target Languages

  • Java - generates a ready-to-publish Maven package.
  • .NET - generates a ready-to-publish NuGet package.
  • Sphinx - generates a Sphinx reStructuredText document for the module with README and reference docs.
  • Python (work in progress) - generates a ready-to-publish PyPI package.
  • Ruby (work in progress) - generates a ready-to-publish RubyGem.

Targets

jsii configuration is read from the jsii section in the module's package.json and includes the following options:

  • targets - the list of target languages this module will be packaged for. For each target, you would need to specify some naming information such as namespaces, package manager coordinates, etc. See supported targets for details.
  • outdir - the default output directory (relative to package root) for jsii-pacmak. This is where target artifacts are emitted during packaging. Each artifact will be emitted under <outdir>/<target> (e.g. dist/java, dist/js, etc). Conventionally we use "dist" for outdir.

Java

The java target will produce a ready-to-deploy Maven package for your jsii module.

The $outdir/java directory will include the contents of a staged offline Maven repository. javadocs and sources are included automatically in the Maven package

This repository can be published to Maven Central via the deploy-staged-repository command of the nexus-staging-maven-plugin. See Sonatype documentation and this gist as a reference.

To package your jsii module for Java, add the following configuration to the jsii section in package.json:

{
  "java": {
    "package": "com.acme.hello",
    "maven": {
      "groupId": "com.acme.hello",
      "artifactId": "hello-jsii"
    }
  }
}

.NET

The dotnet target will produce a ready-to-publish NuGet package for your module.

The $outdir/dotnet directory will include .nupkg files, which can be published to NuGet.

To package your jsii module as for .NET, add this configuration to the jsii section in package.json:

{
  "dotnet": {
    "namespace": "Acme.HelloNamespace", // required
    "packageId": "Acme.HelloPackage",   // required
    "title": "ACME Hello",              // optional (default: packageId)
    "iconUrl": "path/to/icon.svg",      // optional (default: no icon)

    // strong-name signing
    "signAssembly": true,                          // optional (default: false)
    "assemblyOriginatorKeyFile": "path/to/key.snk" // optional
  }
}

Sphinx

The sphinx target emits a Sphinx documentation topic for the module, that can be used to build a Sphinx documentation website. It's not a complete website.

The $outdir/sphinx directory will include two files:

  • <module-name>.rst - the Sphinx topic entry point
  • <module-name>.README.md (optional) - the module's README.md file (if exists)

The .rst file will use m2r to mdinclude the README.md file into the topic.

NOTE: if the first line of your README.md file starts with # (an H1 header), the contents of this line will be used as the first header of the topic. Otherwise, the module's name will be used.

You will need to build a Sphinx documentation website with this .rst included.

To package your jsii module as a Sphinx topic, add an empty object to the jsii section in package.json under the sphinx key:

{
  "sphinx": { }
}

JavaScript

An implicit JavaScript target will always be created. No configuration is needed.

The $outdir/js directory will include that npm tarball of the module (created with npm pack).

Tarballs can be published to npmjs.org using npm publish

What kind of sorcery is this?

So how does this thing work?

Given a source npm module written in one of the supported source languages (currently, only TypeScript is supported as source), we produce a "header file" (called the ".jsii spec") which describes the public API for the module.

Here the .jsii spec for the above example:

{
  "types": {
    "hello-jsii.HelloJsii": {
      "assembly": "hello-jsii",
      "fqn": "hello-jsii.HelloJsii",
      "initializer": {
        "initializer": true
      },
      "kind": "class",
      "methods": [
        {
          "name": "sayHello",
          "parameters": [
            {
              "name": "name",
              "type": {
                "primitive": "string"
              }
            }
          ],
          "returns": {
            "primitive": "string"
          }
        }
      ],
      "name": "HelloJsii",
      "namespace": "hello-jsii"
    }
  }
}

Now, we have two artifacts: the compiled module with .js code and the .jsii spec. This two artifacts are used as input to the next stage we call pacmak (stands for "package maker").

pacmak reads the .jsii spec and module information from package.json and generates a ready-to-publish package artifact for each requested target language. For example, it will produce a Maven package for Java, a NuGet package for .NET, a PyPI module for Python, etc.

The generated packages include proxy classes which represent the API of source module, "translated" to the idioms and conventions of each target language. So if we had a HelloJsii class in the source module with a method sayHello, the .NET generator will emit a HelloJsii class with a method SayHello.

At runtime, when code interacts with proxy classes - creates instances, invokes methods, gets or sets properties - the calls are marshaled in and out to a Node.js VM loaded with the source JavaScript module.

Contributing

See CONTRIBUTING.

License

jsii is distributed under the Apache License, Version 2.0.

See LICENSE and NOTICE for more information.