just use java 21

Author: Project516

app/build.gradle

@@ -12,6 +12,11 @@ plugins {
 
     //Spotless
     id 'com.diffplug.spotless' version '8.0.0'
+    
+    // TeaVM
+    id 'java'
+    id 'war'
+    id "org.teavm" version "0.12.3"
 }
 
 repositories {
@@ -22,6 +27,9 @@ repositories {
 dependencies {
     // This dependency is used by the application.
     implementation libs.guava
+
+    // TeaVM
+    implementation teavm.libs.jsoApis
 }
 
 testing {
@@ -42,11 +50,15 @@ java {
     }
 }
 
+/*
+
 tasks.withType(JavaCompile) {
     // Target Java 8
     options.release.set(8)
 }
 
+*/
+
 application {
     // Define the main class for the application.
     mainClass = 'io.github.project516.NumberGuessingGame.Main'
@@ -61,3 +73,21 @@ spotless {
         removeUnusedImports()
     }
 }
+
+teavm {
+    all {
+        mainClass = "io.github.project516.NumberGuessingGame.Main"
+    }
+    js {
+        addedToWebApp = true
+
+        // this is also optional, default value is <project name>.js
+        targetFileName = "NumberGuessingGame.js"
+    }
+    wasmGC {
+        addedToWebApp = true
+
+        // this is also optional, default value is <project name>.wasm
+        targetFileName = "NumberGuessingGame.wasm"
+    }
+}