diff --git a/.scripts/wpt-mock/XMLHttpRequest.js b/.scripts/wpt-mock/XMLHttpRequest.js
new file mode 100644
index 00000000..e1ac0b16
--- /dev/null
+++ b/.scripts/wpt-mock/XMLHttpRequest.js
@@ -0,0 +1,34 @@
+const fs = require('node:fs');
+const path = require('node:path');
+
+// to be passed to wtp-runner step
+// window.XMLHttpRequest = XMLHttpRequest;
+module.exports = function createXMLHttpRequest(basepath) {
+  return class XMLHttpRequest {
+    constructor() {
+      this._pathname;
+      this.onload;
+      this.onerror;
+      this.response;
+    }
+
+    open(_protocol, url) {
+      this._pathname = url;
+    }
+
+    send() {
+      let buffer;
+
+      try {
+        const pathname = path.join(basepath, this._pathname);
+        buffer = fs.readFileSync(pathname).buffer;
+      } catch (err) {
+        this.onerror(err);
+        return;
+      }
+
+      this.response = buffer;
+      this.onload();
+    }
+  }
+}
diff --git a/.scripts/wpt-mock/wpt-buffer-loader.js b/.scripts/wpt-mock/wpt-buffer-loader.js
new file mode 100644
index 00000000..bc916bb7
--- /dev/null
+++ b/.scripts/wpt-mock/wpt-buffer-loader.js
@@ -0,0 +1,87 @@
+const path = require('node:path');
+
+const createXMLHttpRequest = require('./XMLHttpRequest.js');
+const { OfflineAudioContext } = require('../../index.cjs');
+
+// create a XMLHttpRequest to be passed to the runner
+// can be configured to handle the difference between process.cwd() and given path
+// window.XMLHttpRequest = createXMLHttpRequest(rootURL (?))
+const XMLHttpRequest = createXMLHttpRequest(path.join('examples', 'samples'));
+// maybe should be passed to wtp-runner setup too
+// window.alert = console.log.bind(console);
+const alert = console.log.bind(console);
+
+// this is the BufferLoader from the wpt suite
+function BufferLoader(context, urlList, callback) {
+  this.context = context;
+  this.urlList = urlList;
+  this.onload = callback;
+  this.bufferList = new Array();
+  this.loadCount = 0;
+}
+
+BufferLoader.prototype.loadBuffer = function(url, index) {
+  // Load buffer asynchronously
+  var request = new XMLHttpRequest();
+  request.open("GET", url, true);
+  request.responseType = "arraybuffer";
+
+  var loader = this;
+
+  request.onload = function() {
+    loader.context.decodeAudioData(request.response, decodeSuccessCallback, decodeErrorCallback);
+  };
+
+  request.onerror = function() {
+    alert('BufferLoader: XHR error');
+  };
+
+  var decodeSuccessCallback = function(buffer) {
+    loader.bufferList[index] = buffer;
+    if (++loader.loadCount == loader.urlList.length)
+      loader.onload(loader.bufferList);
+  };
+
+  var decodeErrorCallback = function() {
+    alert('decodeErrorCallback: decode error');
+  };
+
+  request.send();
+}
+
+BufferLoader.prototype.load = function() {
+  for (var i = 0; i < this.urlList.length; ++i)
+    this.loadBuffer(this.urlList[i], i);
+}
+
+// ----------------------------------------------
+// testing
+// ----------------------------------------------
+
+const offlineContext = new OfflineAudioContext({
+  numberOfChannels: 1,
+  length: 1,
+  sampleRate: 48000,
+});
+
+const okFiles = [path.join('sample.wav')];
+const err1Files = [path.join('corrupt.wav')];
+const err2Files = [path.join('donotexists.wav')];
+
+{
+  // should work
+  const loader = new BufferLoader(offlineContext, okFiles, audioBuffer => console.log(audioBuffer));
+  loader.load();
+}
+
+{
+  // should fail - decode error
+  const loader = new BufferLoader(offlineContext, err1Files, audioBuffer => console.log(audioBuffer));
+  loader.load();
+}
+
+{
+  // should fail - file not found
+  const loader = new BufferLoader(offlineContext, err2Files, audioBuffer => console.log(audioBuffer));
+  loader.load();
+}
diff --git a/examples/decoding-legacy.mjs b/examples/decoding-legacy.mjs
new file mode 100644
index 00000000..afba8741
--- /dev/null
+++ b/examples/decoding-legacy.mjs
@@ -0,0 +1,50 @@
+import fs from 'node:fs';
+import path from 'node:path';
+import { AudioContext, OfflineAudioContext } from '../index.mjs';
+
+const latencyHint = process.env.WEB_AUDIO_LATENCY === 'playback' ? 'playback' : 'interactive';
+const audioContext = new AudioContext({ latencyHint });
+
+const offlineContext = new OfflineAudioContext({
+  numberOfChannels: 1,
+  length: 1,
+  sampleRate: audioContext.sampleRate
+});
+
+const okFile = path.join('examples', 'samples', 'sample.wav');
+const errFile = path.join('examples', 'samples', 'corrupt.wav');
+
+function decodeSuccess(buffer) {
+  console.log(`decodeSuccess`);
+  const src = audioContext.createBufferSource();
+  src.buffer = buffer;
+  src.connect(audioContext.destination);
+  src.start();
+}
+
+function decodeError(err) {
+  console.log(`decodeError callback: ${err.message}`);
+}
+
+{
+  // audioContext decode success
+  const okArrayBuffer = fs.readFileSync(okFile).buffer;
+  audioContext.decodeAudioData(okArrayBuffer, decodeSuccess, decodeError);
+  // audioContext decode error
+  const errArrayBuffer = fs.readFileSync(errFile).buffer;
+  audioContext.decodeAudioData(errArrayBuffer, decodeSuccess, decodeError);
+}
+
+await new Promise(resolve => setTimeout(resolve, 3000));
+
+{
+  // offlineContext decode success
+  const okArrayBuffer = fs.readFileSync(okFile).buffer;
+  offlineContext.decodeAudioData(okArrayBuffer, decodeSuccess, decodeError);
+  // offlineContext decode error
+  const errArrayBuffer = fs.readFileSync(errFile).buffer;
+  offlineContext.decodeAudioData(errArrayBuffer, decodeSuccess, decodeError);
+}
+
+await new Promise(resolve => setTimeout(resolve, 3000));
+await audioContext.close();
diff --git a/js/AudioContext.js b/js/AudioContext.js
index 2dbc6ecf..a6d84079 100644
--- a/js/AudioContext.js
+++ b/js/AudioContext.js
@@ -1,3 +1,5 @@
+const { isFunction } = require('./lib/utils.js');
+
 let contextId = 0;
 
 const kProcessId = Symbol('processId');
@@ -45,15 +47,29 @@ module.exports = function(NativeAudioContext) {
       }
     }
 
-    decodeAudioData(audioData) {
+    // This is not exactly what the spec says, but if we reject the promise
+    // when `decodeErrorCallback` is present the program will crash in an
+    // unexpected manner
+    // cf. https://webaudio.github.io/web-audio-api/#dom-baseaudiocontext-decodeaudiodata
+    decodeAudioData(audioData, decodeSuccessCallback, decodeErrorCallback) {
       if (!(audioData instanceof ArrayBuffer)) {
         throw new TypeError(`Failed to execute 'decodeAudioData': parameter 1 is not of type 'ArrayBuffer'`);
       }
+
       try {
         const audioBuffer = super.decodeAudioData(audioData);
-        return Promise.resolve(audioBuffer);
+
+        if (isFunction(decodeSuccessCallback)) {
+          decodeSuccessCallback(audioBuffer);
+        } else {
+          return Promise.resolve(audioBuffer);
+        }
       } catch (err) {
-        return Promise.reject(err);
+        if (isFunction(decodeErrorCallback)) {
+          decodeErrorCallback(err);
+        } else {
+          return Promise.reject(err);
+        }
       }
     }
   }
diff --git a/js/OfflineAudioContext.js b/js/OfflineAudioContext.js
index b9552915..fa80c617 100644
--- a/js/OfflineAudioContext.js
+++ b/js/OfflineAudioContext.js
@@ -1,5 +1,5 @@
 const { NotSupportedError } = require('./lib/errors.js');
-const { isPlainObject, isPositiveInt, isPositiveNumber } = require('./lib/utils.js');
+const { isFunction, isPlainObject, isPositiveInt, isPositiveNumber } = require('./lib/utils.js');
 
 module.exports = function patchOfflineAudioContext(NativeOfflineAudioContext) {
   class OfflineAudioContext extends NativeOfflineAudioContext {
@@ -36,16 +36,29 @@ module.exports = function patchOfflineAudioContext(NativeOfflineAudioContext) {
       }
     }
 
-    decodeAudioData(audioData) {
+    // This is not exactly what the spec says, but if we reject the promise
+    // when `decodeErrorCallback` is present the program will crash in an
+    // unexpected manner
+    // cf. https://webaudio.github.io/web-audio-api/#dom-baseaudiocontext-decodeaudiodata
+    decodeAudioData(audioData, decodeSuccessCallback, decodeErrorCallback) {
       if (!(audioData instanceof ArrayBuffer)) {
         throw new TypeError(`Failed to execute 'decodeAudioData': parameter 1 is not of type 'ArrayBuffer'`);
       }
 
       try {
         const audioBuffer = super.decodeAudioData(audioData);
-        return Promise.resolve(audioBuffer);
+
+        if (isFunction(decodeSuccessCallback)) {
+          decodeSuccessCallback(audioBuffer);
+        } else {
+          return Promise.resolve(audioBuffer);
+        }
       } catch (err) {
-        return Promise.reject(err);
+        if (isFunction(decodeErrorCallback)) {
+          decodeErrorCallback(err);
+        } else {
+          return Promise.reject(err);
+        }
       }
     }
   }
diff --git a/js/lib/utils.js b/js/lib/utils.js
index 61ca06ae..0e4af00d 100644
--- a/js/lib/utils.js
+++ b/js/lib/utils.js
@@ -9,3 +9,8 @@ exports.isPositiveInt = function isPositiveInt(n) {
 exports.isPositiveNumber = function isPositiveNumber(n) {
   return Number(n) === n && 0 < n;
 };
+
+exports.isFunction = function isFunction(val) {
+  return Object.prototype.toString.call(val) == '[object Function]' ||
+    Object.prototype.toString.call(val) == '[object AsyncFunction]';
+}