Migration from CheerpJ 2

CheerpJ 3 is a complete reimplementation of CheerpJ 2, and as such it is not fully backwards compatible.

Script tag

Include CheerpJ 3 on your page with the following snippet:

<script src="https://cjrtnc.leaningtech.com/3.0rc2/cj3loader.js"></script>

Breaking changes

When designing the new architecture we had the objective of making a drop-in replacement for CheerpJ 2.3 as much as we could. This objective has been mostly achieved, but in some cases we had to deprecate and remove functionalities in favor of much improved alternatives.

cheerpjInit is now asynchronous

The runtime API is not exposed until cheerpjInit is called and its Promise resolves.

Therefore, be sure to await the cheerpjInit call before using any other functions.

cheerpj-dom.jar removed

Calling JavaScript functions from Java is now done using the natives option of cheerpjInit. See the JNI guide for more information.

If you used the com.leaningtech.client package extensively, check out the CJDom library (not maintained by Leaning Technologies).

cheerpjRunJarWithClasspath removed

This feature had no real use case because when using java -jar, the JAR file is the source of all user classes, and any other class path settings are ignored.

CheerpJWorker replaced

CheerpJ can now be imported in a Web Worker without any special setup. Simply call importScripts from a worker to load CheerpJ, then use CheerpJ as usual. The CheerpJWorker class has been removed.

// Use CheerpJ as usual
(async () => {
await cheerpjInit();
const lib = await cheerpjRunLibrary("/app/example.jar");
// ...

cjNew and cjCall replaced with library mode API

cjNew and cjCall have been removed in favour of cheerpjRunLibrary.

// CheerpJ 2
let obj = await cjNew("com.library.MyClass");
await cjCall(obj, "myMethod");
// CheerpJ 3
await cheerpjInit();
const lib = await cheerpjRunLibrary("/app/library.jar");
const MyClass = await lib.com.library.MyClass;
const obj = await new MyClass();
await obj.myMethod();

Other major changes

No Ahead-Of-Time compilation (cheerpjify.py)

No Ahead-Of-Time compilation: To achieve good performance, CheerpJ required you to post-process JAR files with a custom binary compiler. The compiler would generate a .jar.js files for each input JAR. CheerpJ 3 features an advanced JIT engine that can generate better-performing code than CheerpJ 2.3 ever could. Removal of .jar.js files also significantly decreases how much data needs to be downloaded during application startup.

No downloads are provided with CheerpJ 3.

  • AOT optimization: CheerpJ 3 uses a JIT compiler only, and as such it does not require any pre-processing of the JAR files, like conversion to .jar.js.
  • --natives: JNI function implementations should be passed to cheerpjInit using the natives option. See the JNI guide for more information.

Actual support for ClassLoaders

CheerpJ 2.3 had very limited support for ClassLoaders. As a consequence of requiring AOT compilation of .jar.js files, it could only support the standard one provided by OpenJDK. CheerpJ 3.0 radically improves the status-quo by properly using ClassLoaders as expected by Java.

com.leaningtech.handlers HTTP handler no longer needed

Previously, CheerpJ 2 required a special Java property to be set in order for HTTP(S) requests to work. This is no longer needed.

cheerpjAddStringFile deprecated and renamed to cheerpOSAddStringFile

The cheerpjAddStringFile function has been renamed to cheerpOSAddStringFile to better reflect its behaviour and provide parity with CheerpX. The old name is still available for backwards compatibility.

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