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Maintenance Announcement: jsii & jsii-rosetta 1.x

Announcement Date: 2023-04-24

We have recently released jsii@5.0.0 and jsii-rosetta@5.0.0, built on the TypeScript 5.0.x compiler, allowing package maintainers to migrate to a more modern TypeScript language version than 3.9 (which the 1.x release line is built on). This change was designed in RFC-374, and removes the need for developers to pin some of their dependencies to releases still compatible with TypeScript 3.9 without necessarily requiring their dependents to do the same at the same time. Upgrading your jsii and jsii-rosetta dependencies to v5.0.x is transparent to your users.

Starting with the 5.0.x release of jsii and jsii-rosetta, we are using a new versioning strategy for these two tools. Going forward we will closely follow new TypeScript compiler releases with new jsii and jsii-rosetta releases, enabling the entire jsii developer community to adopt new TypeScript syntax & benefit from bug fixes and performance enhancements brought into the TypeScript compiler, while retaining the ability control the timeline of these upgrades.

We believe the new versioning strategy will result in an improved developer experience for jsii library maintainers, and have decided to start the process of retiring the 1.x release line. In accordance with our maintenance commitment for the 1.x release line, the retirement timeline is the following:

  • On 2023-04-24, jsii@1.x and jsii-rosetta@1.x will enter the Maintenance Announcement stage. During this stage, they will continue to be actively maintained, including new features back-ported from the current release (5.0.x or later), bug fixes, and security updates.
  • On 2023-10-31 (six months later), the releases will move into the Maintenance stage. During this stage, they will continue receiving bug fixes and security updates, but will no longer receive new features.
  • On 2024-10-31 (one year later), the releases will finally reach End-of-Support, and will no longer receive any features, bug fixes, or security udpates.

Future 1.x releases of jsii and jsii-rosetta will soon start displaying a warning when used, encouraging customers to migrate to the newer releases, which we believe will provide a better experience.

Frequently Asked Questions

How difficult is it to migrate from 1.x to 5.0.x?

The TypeScript language incurred a number of breaking changes between 3.9 and 5.0, including the following:

In addition to these, two import changes affect jsii exported APIs specifically:

  • The 1.x release line silently ignores index signatures (these are hence unavailable in other languages), and the 5.0.x release starts explicitly rejecting these

    • You can explicitly opt into the 1.x behavior by adding the @jsii ignore doc-tag:
      export interface Example {
         * This API is not visible in non-TS/JS languages.
         * @jsii ignore
        readonly [key: string]: any;
  • The 1.x release line incorrectly interprets tuple types as synonyms to object (resulting in those APIs often being unusable from other languages), and the 5.0.x release starts explicitly rejecting these

    • These APIs need to be replaced. You can use the @jsii ignore doc-tag to explicitly opt these APIs out of the multi-language supported API, and provide an alternate API:
      export class Example {
           * @jsii ignore
           * @deprecated Prefer using `newMethod` instead.
          public method(): [string, number] { /* ... */ }
          public newMethod(): StringAndNumber { /* ... */ }
      export interface StringAndNumber {
          readonly stringValue: string;
          readonly numberValue: number;

What happens with other packages of the jsii toolchain (jsii-pacmak, jsii-config, etc...)?

The new versioning strategy only affects the jsii and jsii-rosetta packages. All other parts of the jsii toolchain will continue to be released under the 1.x release line for the foreseeable future. The compilation artifacts produced by jsii@5.0.0 and newer remain compatible with jsii tools from the 1.x toolchain, so developers do not have to coordinate upgrades with their dependents and dependencies.

If I upgrade my package to jsii@5.0.0, are my dependents required to do the same?

You can decide to upgrade your jsii compiler as well as jsii-rosetta independently from your dependencies and dependents. Output artifacts are compatible across all tool releases, including the 1.x line, at least until they reach End-of-Support.

Can my app have dependencies built by different jsii release lines?

The jsii compiler and jsii-rosetta versions used to build a library has no material impact on the runtime artifacts. The underlying runtime platform remains unchanged, and developers do not need to worry about which version of the compiler was used to produce their dependencies.

How often will new jsii & jsii-rosetta release lines be started?

New releases will closely follow those of the TypeScript compiler, which are created approximately once per quarter. While we encourage customers to migrate to the latest release line as quickly as possible, the updated Support & Maintenance Policy for these tools guarantees a minimum of six calendar months of bug fixes and security updates for non-current release lines, so that users can migrate on their own schedule.

What is the support policy for the new 5.0.x and newer releases?

The applicable maintenance and support policy is documented in the file of the aws/jsii-compiler and aws/jsii-rosetta repositories. The main aspects of the new support policy are:

  • Only the latest release line is deemed Current, and receives new features, bug fixes, and security updates;
  • Once a release stops being Current, it moves into Maintenance, where it continues receiving bug fixes and security updates, but no new features will be added;
  • After six (6) months in Maintenance, a release line moves to End-of-Support, and is no longer maintained.

What happens if I continue using releases after they reach End-of-Support?

Once End-of-Support is declared for the releases, we will no longer be able to provide support, bug fixes, or security updates for these releases. You may elect to continue to use them at your discretion (published releases will remain available to download from the package registry indefinitely). You should be aware that, although there is no plan to introduce non-backwards compatible features at this stage, it is possible that some of your library’s dependencies may stop being compatible with 1.x releases of the compiler in the future, and your library’s dependents may at some point no longer be able to consume 1.x compiler output artifacts.