Compiling for the Web

Requirements

To compile export templates for the Web, the following is required:

• Emscripten 1.38.27+: If the version available per package manager is not recent enough, the best alternative is to install using the Emscripten SDK
• Python 2.7+ or Python 3.5+
• SCons build system

See also

For a general overview of SCons usage for Godot, see Introduction to the buildsystem.

Building export templates

Before starting, confirm that the Emscripten configuration file exists and specifies all settings correctly. This file is available as ~/.emscripten on UNIX-like systems and %USERPROFILE%\.emscripten on Windows. It’s usually written by the Emscripten SDK, e.g. when invoking emsdk activate latest, or by your package manager. It’s also created when starting Emscripten’s emcc program if the file doesn’t exist.

Attention

On Windows, make sure to escape backslashes of paths within the Emscripten configuration file as double backslashes \\ or use Unix-style paths with a single forward slash /.

Open a terminal and navigate to the root directory of the engine source code. Then instruct SCons to build the JavaScript platform. Specify target as either release for a release build or release_debug for a debug build:

scons platform=javascript tools=no target=release
scons platform=javascript tools=no target=release_debug

By default, the JavaScript singleton will be built into the engine. Since eval() calls can be a security concern, the javascript_eval option can be used to build without the singleton:

scons platform=javascript tools=no target=release javascript_eval=no
scons platform=javascript tools=no target=release_debug javascript_eval=no

The engine will now be compiled to WebAssembly by Emscripten. Once finished, the resulting file will be placed in the bin subdirectory. Its name is godot.javascript.opt.zip for release or godot.javascript.opt.debug.zip for debug.

Finally, rename the zip archive to webassembly_release.zip for the release template:

mv bin/godot.javascript.opt.zip bin/webassembly_release.zip

And webassembly_debug.zip for the debug template:

mv bin/godot.javascript.opt.debug.zip bin/webassembly_debug.zip

Building per asm.js translation or LLVM backend

WebAssembly can be compiled in two ways: The default is to first compile to asm.js, a highly optimizable subset of JavaScript, using Emscripten’s fastcomp fork of LLVM. This code is then translated to WebAssembly using a tool called asm2wasm. Emscripten automatically takes care of both processes, we simply run SCons.

The other method uses LLVM’s WebAssembly backend. This backend is available starting with LLVM 8 or in development builds. Emscripten manages this process as well, so we just invoke SCons.

In order to choose one of the two methods, the LLVM_ROOT variable in the Emscripten configuration file is used. If it points to a directory containing binaries of Emscripten’s fastcomp fork of clang, asm2wasm is used. This is the default in a normal Emscripten installation. Otherwise, LLVM binaries built with the WebAssembly backend will be expected and the LLVM’s WebAssembly backend is used.