tree: 057909e068fdd0d66ae8dedbaaf6e3a8887dce73 [path history] [tgz]
  1. index.html
  2. index_wasm.html
  4. test_webp_js.webp
  5. test_webp_wasm.webp

WebP JavaScript decoder

 __   __ ____ ____ ____     __  ____
/  \\/  \  _ \  _ \  _ \   (__)/  __\
\       /  __/ _  \  __/   _)  \_   \
 \__\__/_____/____/_/     /____/____/

This file describes the compilation of libwebp into a JavaScript decoder using Emscripten and CMake.

  • install the Emscripten SDK following the procedure described at: After installation, you should have some global variable positioned to the location of the SDK. In particular, $EMSDK should point to the top-level directory containing Emscripten tools.

  • configure the project ‘WEBP_JS’ with CMake using:

    cd webp_js && \
    emcmake cmake -DWEBP_BUILD_WEBP_JS=ON ../
  • compile webp.js using ‘emmake make’.

  • that's it! Upon completion, you should have the ‘webp.js’, ‘webp.js.mem’, ‘webp_wasm.js’ and ‘webp_wasm.wasm’ files generated.

The callable JavaScript function is WebPToSDL(), which decodes a raw WebP bitstream into a canvas. See webp_js/index.html for a simple usage sample (see below for instructions).

Demo HTML page

The HTML page webp_js/index.html requires the built files ‘webp.js’ and ‘webp.js.mem’ to be copied to webp_js/. An HTTP server to serve the WebP image example is also needed. With Python, just run:

cd webp_js && python3 -m http.server 8080

and then navigate to http://localhost:8080 in your favorite browser.

Web-Assembly (WASM) version:

CMakeLists.txt is configured to build the WASM version when using the option WEBP_BUILD_WEBP_JS=ON. The compilation step will assemble the files ‘webp_wasm.js’ and ‘webp_wasm.wasm’ that you then need to copy to the webp_js/ directory.

See webp_js/index_wasm.html for a simple demo page using the WASM version of the library.


  • First decoding using the library is usually slower, due to just-in-time compilation.