Early access of graalvm, version 25 can build #java to #wasm <a href="https://stackoverflow.com/a/79542976/175554" target="_blank" rel="noopener nofollow">here</a> is how to do it.
<pre><code>ozkan@HP-ENVY-2021-I7 C:\tmp
$ native-image --tool:svm-wasm HelloWasm
============================================================================================================

GraalVM Native Image: Generating &#x27;hellowasm.exe&#x27; (executable)...
============================================================================================================

For detailed information and explanations on the build output, visit:
https://github.com/oracle/graal/blob/master/docs/reference-manual/native-image/BuildOutput.md
------------------------------------------------------------------------------------------------------------

[1/8] Initializing... (29.1s @ 0.15GB)

 Java version: 25+14-LTS, vendor version: Oracle GraalVM 25-dev+14.1
 Graal compiler: optimization level: 2, target machine: unknown, PGO: off
 C compiler: cl.exe (microsoft, x64, 19.43.34809)
 Garbage collector: JS-runtime-provided GC (max heap size: unknown)
 1 user-specific feature(s):
 - com.oracle.svm.thirdparty.gson.GsonFeature
------------------------------------------------------------------------------------------------------------

Build resources:
 - 12.79GB of memory (75.6% of system memory, less than 8GB of memory available)
 - 8 thread(s) (100.0% of 8 available processor(s), determined at start)
Warning: We could not find any version info for the following classes:
org.graalvm.aotjs.api.JSError
org.graalvm.aotjs.api.JSBoolean
org.graalvm.aotjs.api.JSNumber
org.graalvm.aotjs.api.JSUndefined
org.graalvm.aotjs.api.JSObject
org.graalvm.aotjs.api.JSSymbol
org.graalvm.aotjs.api.JSString
HelloWasm
org.graalvm.aotjs.api.JSValue
org.graalvm.aotjs.api.JSBigInt
[2/8] Performing analysis... [***] (12.1s @ 0.18GB)

 1,018 reachable types (43.5% of 2,340 total)
 745 reachable fields (29.4% of 2,534 total)
 3,111 reachable methods (20.1% of 15,456 total)
 408 types, 31 fields, and 111 methods registered for reflection
[3/8] Building universe... (2.2s @ 0.23GB)

[4/8] Parsing methods... [*] (1.0s @ 0.19GB)

[5/8] Inlining methods... [***] (0.7s @ 0.21GB)

[6/8] Compiling methods... [**] (3.0s @ 0.23GB)

[7/8] Laying out methods... [*] (0.3s @ 0.24GB)

[8/8] Creating image... [***] (9.3s @ 0.26GB)

 0.00B ( 0.00%) for code area: 1,630 compilation units
 672.71kB (60.25%) for image heap: 9,174 objects and 9 resources
 443.90kB (39.75%) for other data
 1.12MB in total
------------------------------------------------------------------------------------------------------------

Top 10 origins of code area: Top 10 object types in image heap:
 0.00B org.graalvm.collections 130.88kB byte[] for java.lang.String
 0.00B org.graalvm.extraimage.builder 130.30kB com.oracle.svm.core.hub.DynamicHubCompanion
 0.00B com.oracle.svm.svm_enterprise 107.00kB java.lang.Class
 0.00B svm.jar (Native Image) 70.09kB char[]
 0.00B org.graalvm.webimage.api 66.82kB java.lang.String
 0.00B jdk.graal.compiler 21.17kB c.o.s.c.hub.DynamicHub$ReflectionMetadata
 0.00B jdk.proxy3 15.52kB byte[] for general heap data
 0.00B jdk.proxy1 15.05kB byte[] for reflection metadata
 0.00B jdk.proxy2 13.06kB c.o.s.c.configure.ConditionalRuntimeValue
 0.00B java.base 12.35kB java.lang.String[]
 0.00B for 1 more packages 90.48kB for 187 more object types
 Use &#x27;--emit build-report&#x27; to create a report with more details.
------------------------------------------------------------------------------------------------------------

Security report:
 - Binary includes Java deserialization.
 - CycloneDX SBOM with 6 component(s) is embedded in binary (486.00B).
------------------------------------------------------------------------------------------------------------

Recommendations:
 PGO: Use Profile-Guided Optimizations (&#x27;--pgo&#x27;) for improved throughput.
 HEAP: Set max heap for improved and more predictable memory usage.
 CPU: Enable more CPU features with &#x27;-march=native&#x27; for improved performance.
 QBM: Use the quick build mode (&#x27;-Ob&#x27;) to speed up builds during development.
------------------------------------------------------------------------------------------------------------

 2.1s (3.2% of total time) in 60 GCs | Peak RSS: 874.91MB | CPU load: 3.87
------------------------------------------------------------------------------------------------------------

Build artifacts:
 C:\tmp\hellowasm.js (executable)
 C:\tmp\hellowasm.js.wasm (executable)
 C:\tmp\hellowasm.js.wat (build_info)
============================================================================================================

Finished generating &#x27;hellowasm&#x27; in 59.9s.

ozkan@HP-ENVY-2021-I7 C:\tmp
$ node hellowasm.js
Özkan was here :) Hello from WebAssembly generated with GraalVM!

ozkan@HP-ENVY-2021-I7 C:\tmp
$ type HelloWasm.java
 public class HelloWasm {
 public static void main(String[] args) {
 System.out.println(&quot;├ûzkan was here :) Hello from WebAssembly generated with GraalVM!&quot;);
 }
 }
ozkan@HP-ENVY-2021-I7 C:\tmp
$
</code></pre>
in case you wonder how to run wasm from java here is example
<pre><code>try (Context context = Context.create()) {
	URL wasmFile = WasmdemoApplication.class.getResource(&quot;/test.wasm&quot;);
	String moduleName = &quot;main&quot;;
	context.eval(Source.newBuilder(&quot;wasm&quot;, wasmFile).name(moduleName).build());
	Value addTwo = context.getBindings(&quot;wasm&quot;).getMember(moduleName).getMember(&quot;addTwo&quot;);
	return &quot;addTwo(40, 2) = &quot; + addTwo.execute(40, 2);
} catch (IOException e) {
	throw new RuntimeException(e);
}
</code></pre>
Full code <a href="https://github.com/ozkanpakdil/spring-examples/blob/master/wasmdemo" target="_blank" rel="noopener nofollow">here</a>

All Java, All the time.

Newcomers to veterans, all are welcome to post and comment about anything Java related. Love it, hate it - all topics are safe here. 

Just Java

GraalVM version 25 early access allows building Java applications into WebAssembly (Wasm). The process involves running a native image command to generate Wasm executables. The post includes a step-by-step example demonstrating the conversion of a Java class to Wasm and how to execute the resulting Wasm file using Node.js.

How to build java to wasm

what is the size of the wasm for this ?