local objectData = {
    [1] = {txd="1.txd", dff="1.dff"},
    [2] = {txd="2.txd", dff="2.dff"},
    [5] = {txd="5.txd", dff="5.dff"}
}

local downloadStatus = {}

function init()
    --Loop our object data, and intiliaze a download "state"
    for id, data in pairs(objectData) do
        downloadStatus[id] = {}
        downloadStatus[id].txd, downloadStatus[id].dff = false, false

        --Start downloading
        downloadFile(data.txd)
        downloadFile(data.dff)
    end
end
addEventHandler("onClientResourceStart", resourceRoot, init) --As an example, start with the resource

function handleObjectDownloads(file, success)
    --If the file wasn't downloaded, return with an error message
    if not success then
        return outputDebugString("Download failed for "..file)
    end

    --We could make this more efficient, but for simplicity I'll keep it like this
    --Loop through all the object data and check if the object "package" has been downloaded, else, store the download completion state for this file.
    local id, filetype
    for i, data in pairs(objectData) do
        if data.txd == file then
            filetype = "txd"
        elseif data.dff == file then
            filetype = "dff"
        end

        if filetype then
            id = i
        end
    end

    --The file downloaded is not relevant
    if not id then
        return false
    end

    --Set download status for this file to true
    downloadStatus[id][filetype] = true

    --If all the files aren't downloaded yet, then return and wait
    for i, status in ipairs(downloadStatus[id]) do
        if not status then
            return false
        end
    end

    --All files in this "package" are downloaded, so import the txd/dffs
    local txd = engineLoadTXD(objectData[id].txd)
    engineImportTXD(txd, id)

    local dff = engineLoadDFF(objectData[id].dff, id)
    engineReplaceModel(dff, id)

    return true
end
addEventHandler("onClientFileDownloadComplete", root, handleObjectDownloads)