This plugin works on iOS, Windows Phone 8 and Android: http://plugreg.com/plugin/whiteoctober/cordova-plugin-app-version
If you're using the Cordova CLI, you can install via:
cordova plugin add https://github.com/whiteoctober/cordova-plugin-app-version.git
Then it's as simple as:
cordova.getAppVersion(function (version) {
alert(version);
});
(after the device ready function has been fired)