My current version looks like this (WIP!) Maybe it is helpful for you:

// Android 8.1.0 / API Level 27

// HIER AKTUALISIEREN!!!
const allowedVersions = ["02-52-21.00-OG-U01-STD", "02-52-21.00-OG-U02-STD", "02-52-21.00-OG-U03-STD"];

// Initialisierung des Zebra Lifeguard Updates
mobicontrol.log.info("#MST - Initiate Zebra Lifeguard Update");

// Ermittlung der aktuellen Version
const buildNumber = mobicontrol.os.buildNumber;
mobicontrol.log.info("#MST - Current Version: " + buildNumber);
const osNumber = mobicontrol.os.apiLevel;
mobicontrol.log.info("#MST - Current API Level: " + osNumber);

// Ermittlung des Batteriestatus, Ladezustands und verfügbaren Speicherplatzes
const batteryLevel = mobicontrol.battery.level;
const isCharging = mobicontrol.battery.isCharging;
const availableSpace = mobicontrol.storage.internal.availableSpace / 1073741824;

const lastAllowedVersion = allowedVersions[allowedVersions.length - 1];

// Überprüfung, ob die aktuelle Version Teil des Major Releases ist
if (allowedVersions.includes(buildNumber)) {
    mobicontrol.log.info("#MST - Current version is part of the major release, searching for possible delta updates");
    DeltaUpdateLifeguard();
} else {
    mobicontrol.log.info("#MST - Initial version too low - Starting Full Update");
    UpdateLifeguard();
}

// Durchführung des Delta Updates
function DeltaUpdateLifeguard() {
    // Überprüfung der erforderlichen Voraussetzungen für das Zebra Lifeguard Update
    if ((batteryLevel >= 0.50 || isCharging) && availableSpace >= 1 && osNumber === 27) {
        mobicontrol.log.info("#MST - Necessary requirements for Zebra Lifeguard update fulfilled");

        // Überprüfung, ob ein neues Delta Update verfügbar ist
        if (buildNumber !== lastAllowedVersion) {
            mobicontrol.log.info("#MST - New Delta Update available");
            const fileNameDelta = 'ATLAS_DELTA_UPDATE_' + lastAllowedVersion.split('-').join('_') + '.zip';
            mobicontrol.log.info(fileNameDelta);
        } else {
            mobicontrol.log.info("#MST - No further Delta Update available");
        }
    } else {
        mobicontrol.log.warn("#MST - Necessary hardware requirements for Zebra Lifeguard update not fulfilled");
    }
}

// Durchführung des Major Updates
function UpdateLifeguard() {
    // Überprüfung der erforderlichen Voraussetzungen für das Zebra Lifeguard Update
    if ((batteryLevel >= 0.50 || isCharging) && availableSpace >= 1 && osNumber === 27) {
        mobicontrol.log.info("#MST - Necessary requirements for Zebra Lifeguard update fulfilled");

        // Ermittlung des Major Releases
        const firstAllowedVersion = allowedVersions[0];
        mobicontrol.log.info("#MST - Major Release: " + firstAllowedVersion);

        // Generierung des Dateinamens für das Full Update
        const fileNameFull = 'FPU_ATLAS_' + firstAllowedVersion.split('-').join('_') + '.zip';
        mobicontrol.log.info("#MST - Full Update file name: " + fileNameFull);
    } else {
        mobicontrol.log.warn("#MST - Something went wrong");
    }
}