Newbie question: How to create a namespace and record filedate-retrieve

Question

Spanking new to Namespaces
Looking for a way to place a .jpg as a smart object, then using Namespace, record the filedate of the .jpg
Then, have the layer sense if the original .jpg is newer and change the color of the layer.
Running into complications trying to do this with .jsx scripting alone.
Reason: This way, if the .jpg has been updated on the file server, the artist will be able to easily see that.
Don't want to add a panel and more work for the artist. Rather, have it all happen behind the scenes.

Answer 1

Here is how I create a new namespace in the layer metadata for my panel
// new namespace. Even though it looks like a web url it's not. It just needs to be unique.
const ns= 'http://www.smartobjectlinks.com/1.0/';
function setSOLinkMetadata( property, value ){
     if( activeDocument.activeLayer.isBackgroundLayer || !loadXMPLibrary()){
          alert( ErrStrs.CONVERT );
     } else {
          var xmp;
          if (value == "")
               value = " ";     
          try{
               xmp = new XMPMeta( activeDocument.activeLayer.xmpMetadata.rawData );
          } catch(e) {// no metadata so create new and add namespace
               xmp = new XMPMeta();
               var linkNS = new Namespace ( 'link', ns );
               XMPMeta.registerNamespace ( linkNS, 'SOlink' );
          try{
               xmp.setProperty(ns, property, value );
          } catch(e) {
               alert( ErrStrs.FAILEDMETADATA + e);
          activeDocument.activeLayer.xmpMetadata.rawData = xmp.serialize();
     unloadXMPLibrary();
If the file being linked has metadata you can use the ModifyDate in the XMP.
function getfileDate( file ){
     var date = new String();
     try{
          loadXMPLibrary();
          var xmpf = new XMPFile( file.fsName, XMPConst.UNKNOWN,
                                   XMPConst.OPEN_FOR_READ );
          var xmp = xmpf.getXMP();
          xmpf.closeFile();
          date = new XMPDateTime( xmp.getProperty
                              (XMPConst.NS_XMP, "ModifyDate").toString() );
     }catch(e){// fallback to OS file date
          date = new XMPDateTime ( file.created );
     date = date.toString();
     unloadXMPLibrary();
     return date;
The hard part will be getting the layer to 'sense' when the original has been changed. If you don't want the user to trigger the test you will have to use an event like open.