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function getAndroidVersion() {
    var androidVersion = -1; // def value, for non-Android devices
    var ua = navigator.userAgent.toLowerCase();
    var androidIndex = ua.indexOf('android');

    if(androidIndex != -1) {
        var versionStartIndex = androidIndex + 8;
        var versionEndIndex = ua.indexOf(';', versionStartIndex);

        androidVersion = parseFloat(ua.slice(versionStartIndex, versionEndIndex));
    }

    return androidVersion;
}