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--- a/webp_js/README.md
+++ b/webp_js/README.md
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+# 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:
+    https://emscripten.org/docs/getting_started/downloads.html#installation-instructions-using-the-emsdk-recommended
+    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:
+
+    ```shell
+    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:
+
+```shell
+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.
+
+You will need a fairly recent version of Emscripten (at least 2.0.18,
+latest-upstream is recommended) and of your WASM-enabled browser to run this
+version.
+
+## Caveats
+
+-   First decoding using the library is usually slower, due to just-in-time
+    compilation.
+
+-   Some versions of llvm produce the following compile error when SSE2 is
+    enabled.
+
+    ```
+    "Unsupported:   %516 = bitcast <8 x i16> %481 to i128
+    LLVM ERROR: BitCast Instruction not yet supported for integer types larger than 64 bits"
+    ```
+
+    The corresponding Emscripten bug is at:
+    https://github.com/kripken/emscripten/issues/3788
+
+    Therefore, SSE2 optimization is currently disabled in CMakeLists.txt.
+
+-   If WEBP_ENABLE_SIMD is set to 1 the JavaScript version (webp.js) will be
+    disabled as wasm2js does not support SIMD.
--- a/webp_js/index.html
+++ b/webp_js/index.html
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+<!DOCTYPE html>
+<html lang="en">
+
+<head>
+  <meta charset="UTF-8">
+  <title>simple Javascript WebP decoding demo</title>
+  <script type="text/javascript">
+    var Module = {
+      noInitialRun : true
+    };
+  </script>
+  <script type="text/javascript" src="./webp.js"></script>
+  <script type="text/javascript">
+
+'use strict';
+
+// main wrapper for the function decoding a WebP into a canvas object
+var WebpToCanvas;
+
+function init() {
+  WebpToCanvas = Module.cwrap('WebPToSDL', 'number', ['array', 'number']);
+}
+window.onload = init;
+
+function decode(webp_data, canvas_id) {
+  // get the canvas to decode into
+  var canvas = document.getElementById(canvas_id);
+  if (canvas == null) return;
+  // clear previous picture (if any)
+  Module.canvas = canvas;
+  canvas.getContext('2d').clearRect(0, 0, canvas.width, canvas.height);
+  // decode and measure timing
+  var start = new Date();
+  var ret = WebpToCanvas(webp_data, webp_data.length);
+  var end = new Date();
+  var speed_result = document.getElementById('timing');
+  // display timing result
+  if (speed_result != null) {
+    var decode_time = end - start;
+    speed_result.innerHTML = '<p>decoding time: ' + decode_time +' ms.</p>';
+  }
+}
+
+function loadfile(filename, canvas_id) {
+  var xhr = new XMLHttpRequest();
+  xhr.open('GET', filename);
+  xhr.responseType = 'arraybuffer';
+  xhr.onreadystatechange = function() {
+    if (xhr.readyState == 4 && xhr.status == 200) {
+      var webp_data = new Uint8Array(xhr.response);
+      decode(webp_data, canvas_id);
+    }
+  };
+  xhr.send();
+}
+  </script>
+</head>
+
+<body>
+  <p>
+    <strong>WebP in JavaScript demo</strong> -
+  </p>
+  <p>
+    WebP decoder in JavaScript, using libwebp compiled with
+    <a href="https://github.com/kripken/emscripten/wiki">Emscripten</a>.
+  </p>
+  <p id="image_buttons">
+    <input type="button" value="test image!" name="./test_webp_js.webp"
+           onclick="loadfile(this.name, 'output_canvas')">
+  </p>
+  <p id="timing">Timing: N/A</p>
+  <canvas id="output_canvas">Your browser does not support canvas</canvas>
+
+</body>
+</html>
--- a/webp_js/index_wasm.html
+++ b/webp_js/index_wasm.html
@ -0,0 +1,90 @@
+<!DOCTYPE html>
+<html lang="en">
+
+<head>
+  <meta charset="UTF-8">
+  <title>simple Javascript WebP decoding demo, using Web-Assembly (WASM)</title>
+  <script type="text/javascript">
+    var Module = {
+      noInitialRun : true
+    };
+  </script>
+  <script type="text/javascript">
+
+'use strict';
+
+// main wrapper for the function decoding a WebP into a canvas object
+var WebpToCanvas;
+
+function init() {
+  var xhr = new XMLHttpRequest();
+  xhr.open('GET', 'webp_wasm.wasm', true);
+  xhr.responseType = 'arraybuffer';
+  xhr.onload = function() {
+    Module.wasmBinary = xhr.response;
+    var script = document.createElement('script');
+    script.src = "webp_wasm.js";
+    document.body.appendChild(script);
+  };
+  xhr.send(null);
+}
+window.onload = init;
+
+function decode(webp_data, canvas_id) {
+  var result;
+  if (Module["asm"] != undefined) {
+    // wrapper for the function decoding a WebP into a canvas object
+    WebpToCanvas = Module.cwrap('WebPToSDL', 'number', ['array', 'number']);
+    // get the canvas to decode into
+    var canvas = document.getElementById(canvas_id);
+    if (canvas == null) return;
+    // clear previous picture (if any)
+    Module.canvas = canvas;
+    canvas.getContext('2d').clearRect(0, 0, canvas.width, canvas.height);
+    // decode and measure timing
+    var start = new Date();
+    var ret = WebpToCanvas(webp_data, webp_data.length);
+    var end = new Date();
+    var decode_time = end - start;
+    result = 'decoding time: ' + decode_time +' ms.';
+  } else {
+    result = "WASM module not finished loading! Please retry";
+  }
+  // display timing result
+  var speed_result = document.getElementById('timing');
+  if (speed_result != null) {
+    speed_result.innerHTML = '<p>'+ result + '</p>';
+  }
+}
+
+function loadfile(filename, canvas_id) {
+  var xhr = new XMLHttpRequest();
+  xhr.open('GET', filename);
+  xhr.responseType = 'arraybuffer';
+  xhr.onreadystatechange = function() {
+    if (xhr.readyState == 4 && xhr.status == 200) {
+      var webp_data = new Uint8Array(xhr.response);
+      decode(webp_data, canvas_id);
+    }
+  };
+  xhr.send();
+}
+  </script>
+</head>
+
+<body>
+  <p>
+    <strong>WebP demo using Web-Assembly</strong> -
+  </p>
+  <p>
+    WASM version of the WebP decoder, using libwebp compiled with
+    <a href="https://github.com/kripken/emscripten/wiki">Emscripten</a>.
+  </p>
+  <p id="image_buttons">
+    <input type="button" value="test image!"
+           onclick="loadfile('./test_webp_wasm.webp', 'output_canvas')">
+  </p>
+  <p id="timing">Timing: N/A</p>
+  <canvas id="output_canvas">Your browser does not support canvas</canvas>
+</body>
+</html>
--- a/webp_js/test_webp_js.webp
+++ b/webp_js/test_webp_js.webp
--- a/webp_js/test_webp_wasm.webp
+++ b/webp_js/test_webp_wasm.webp