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Eaglercraft compiles the Minecraft 1.5.2 Java codebase to JavaScript using TeaVM via a Gradle build. The primary output is classes.js (the browser client) and classes_server.js (the integrated singleplayer server worker). Custom resource packs are compiled separately as EPK files.

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How the Build Works

The build.gradle file applies the io.github.zebalu.teavm-gradle-plugin (version 1.0.0) to transpile Java source into optimized JavaScript. Key details of the build configuration:
  • Java compatibility: Source and target are both set to Java 8
  • Source sets: Three directories are combined into a single main source set:
    • src/main/java — shared Minecraft client classes
    • src/teavm/java — TeaVM-specific adapter and entry point
    • sp-server/src/ipc/java — singleplayer server IPC bridge
  • Main class: net.lax1dude.eaglercraft.Client (defined in src/teavm/java)
  • Entry point name: main
  • Output file: javascript/classes.js
  • Optimization level: ADVANCED — produces highly compact, aggressively inlined output
  • Heap size: 4 MB minimum / 128 MB maximum for the TeaVM virtual machine

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Prerequisites

Before building, ensure the following are installed:
  • Java JDK 8 — a full JDK is required (not just a JRE); TeaVM performs bytecode analysis at compile time
  • Gradle — you can use the included gradlew / gradlew.bat wrapper and do not need a separate Gradle installation

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Compiling the JavaScript Client

1

Clone the repository

git clone https://github.com/lDEVinux/eaglercraft.git
cd eaglercraft
2

Run the TeaVM compile target

On Linux or macOS:
./gradlew teavm
On Windows:
gradlew.bat teavm
3

Wait for compilation to finish

The ADVANCED optimization level performs thorough whole-program analysis and inlining. Expect the build to take several minutes depending on your hardware.
4

Locate the compiled output

Once the build completes successfully, the output files appear at:
  • javascript/classes.js — the compiled browser client
  • javascript/classes.js.map — the source map for debugging
The LWJGL desktop runtime (src/lwjgl/) is no longer supported and is included in the repository for historical reference only. Only the TeaVM (web) compilation target should be used.

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Compile Configuration

The following block shows the key TeaVM settings from build.gradle:
build.gradle
teavm {
   minifying = true
   maxTopLevelNames = 10000
   debugInformationGenerated = false
   sourceMapsGenerated = true
   targetDirectory = file("javascript")
   targetFileName = "classes.js"
   mainClass = 'net.lax1dude.eaglercraft.Client'
   entryPointName = 'main'
   optimizationLevel = "ADVANCED"
   minHeapSize = 4
   maxHeapSize = 128
}

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Compiling Resource Packs (EPK)

Game assets (textures, sounds, and other resources) are stored in lwjgl-rundir/resources/ and must be compiled into a single assets.epk archive that the browser client loads at runtime. The epkcompiler/run.bat script calls: 
java -jar epkcompiler/CompilePackage.jar "lwjgl-rundir/resources" "javascript/assets.epk"
Run the appropriate script for your platform from the repository root: 
CompileEPK.bat
The compiled asset pack is written to javascript/assets.epk.

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Deploying Compiled Output

After a successful build, copy the following files to your web server to replace the pre-built stable-download versions:
  • javascript/classes.js
  • javascript/assets.epk
Do NOT commit javascript/classes.js, javascript/classes_server.js, javascript/assets.epk, or any files in stable-download/ to pull requests. The project maintainer recompiles all generated artifacts after merging source changes.

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