The play method which the HTML5 API provides is useful for playing media files available on the web. Phonegap provides the media plugin to play local media files. I checked out your code and played the sound successfully by making the following changes. Please check at your end.
1.Add the following line to config.xml
<gap:plugin name="org.apache.cordova.media" />
2.Replace the lines in index.html
<button onclick="document.getElementById('successSound').play()">Play successSound local</button>
<button onclick="document.getElementById('errorSound').play()">Play errorSound local</button>
with these lines
<button onclick="playAudio('successSound')">Play successSound local</button>
<button onclick="playAudio('errorSound')">Play errorSoundlocal</button>
3.Add the following function to js/index.js
function playAudio(id) {
var audioElement = document.getElementById(id);
var url = audioElement.getAttribute('src');
var my_media = new Media(url,
// success callback
function () { console.log("playAudio():Audio Success"); },
// error callback
function (err) { console.log("playAudio():Audio Error: " + err); }
);
// Play audio
my_media.play();
}