I think that "mimeType_query" is used for "searchFiles" method.
Ref But "driveLOC.searchFiles(mimeType_query)" is required to be modified. Because "driveLOC" cannot be directly used as "while (driveLOC.hasNext())". And, I thought that "mimeType_query" is required to be modified. So in your script, how about the following modification?
var mimeType_query = "mimeType = 'application/vnd.google-apps.spreadsheet' or mimeType = 'application/vnd.google-apps.document' or mimeType = 'application/vnd.google-apps.presentation' or mimeType = 'application/pdf'";
var driveLOC = DriveApp.getFolderById("###folderId###").searchFiles(mimeType_query);
while (driveLOC.hasNext()) {
var drive_File = driveLOC.next();
console.log(drive_File.getName());
}