Why doesn't this code work in my extension? Retrieving generator settings from meta data

Question

Using the code below in my host.jsx file within my html 5 extension this code doesnt work:
$._photoshop.setDocumentData('project.isXUI','true');
alert($._photoshop.getDocumentData('project.isXUI'));
Here's the error I get:
Error: The requested property does not exist.
It works perfectly from ExtendScript but the same lines of code do not work when called via "window.__adobe_cep__.evalScript". What am I missing?
$._photoshop = {
setDocumentData: function(key,value)
        try
            var classProperty = charIDToTypeID('Prpr');
            var propNull = charIDToTypeID( 'null' );
            var classNull = charIDToTypeID( 'null' );
            var typeOrdinal = charIDToTypeID('Ordn');
            var enumTarget = charIDToTypeID('Trgt');
            var classDocument = charIDToTypeID('Dcmn');
            var classLayer = charIDToTypeID('Lyr ');
            var propProperty = stringIDToTypeID("property");
            var propGeneratorSettings = stringIDToTypeID("generatorSettings");
            var propProperty = stringIDToTypeID(key); //unique name for the setting
            var keyTo = charIDToTypeID( 'T   ' );
            var actionSet = charIDToTypeID( "setd" );
            //Make a property reference to generator settings for active layer.
            //(use classDocument for the active document)
            //NOTE: putProperty needs to come before putEnumerated
            var theRef = new ActionReference();
            theRef.putProperty(classProperty, propGeneratorSettings );
            theRef.putEnumerated(classDocument, typeOrdinal, enumTarget);
            //Build descriptor for your plugin settings, with 2 example settings, a boolean and a string
            var mySettingsDesc = new ActionDescriptor();
            mySettingsDesc.putString(propProperty,value);
            //Execute the set action, setting the descriptor into the property reference,
            //setting just the plugin's settings (propProperty == strMySettings)
            var setDescriptor = new ActionDescriptor();
            setDescriptor.putReference(propNull,theRef);
            setDescriptor.putObject(keyTo,classNull,mySettingsDesc);
            setDescriptor.putString(propProperty, "au.com.oddgames.xui");
            executeAction( actionSet, setDescriptor, DialogModes.NO );
            return true;
        catch (e)
            var exception = {};
            exception.target = "setDocumentdata";
            exception.message = e.toString();
            return exception;
    getDocumentData: function(key)
        try
            var classProperty = charIDToTypeID('Prpr');
            var propNull = charIDToTypeID( 'null' );
            var classNull = charIDToTypeID( 'null' );
            var typeOrdinal = charIDToTypeID('Ordn');
            var enumTarget = charIDToTypeID('Trgt');
            var classDocument = charIDToTypeID('Dcmn');
            var classLayer = charIDToTypeID('Lyr ');
            var propProperty = stringIDToTypeID("property");
            var propGeneratorSettings = stringIDToTypeID("generatorSettings");
            var propProperty = stringIDToTypeID(key); //unique name for the setting
            var actionGet = charIDToTypeID( "getd" );
            //Make a property reference to generator settings for active layer.
            //(use classDocument for the active document)
            //NOTE: putProperty needs to come before putEnumerated
            var theRef = new ActionReference();
            theRef.putProperty(classProperty, propGeneratorSettings );
            theRef.putEnumerated(classDocument, typeOrdinal, enumTarget);
            //Execute the get action, getting the descriptor for the property reference,
            //getting just the plugin's settings (propProperty == strMySettings)
            var getDescriptor = new ActionDescriptor();
            getDescriptor.putReference(propNull,theRef);
            getDescriptor.putString(propProperty, "au.com.oddgames.xui");
            var actionResult = executeAction( actionGet, getDescriptor, DialogModes.NO );
            //Extract the settings
            var mySettingsDesc = actionResult.getObjectValue(propGeneratorSettings);
            return mySettingsDesc.getString(propProperty);
        catch (e)
            var exception = {};
            exception.target = "getDocumentData";
            exception.message = e.toString();
            return exception

Answer 1

Ok got it, I have to make sure I pull the descriptor back then save my settings over the top:
$._photoshop = {
    setDocumentData: function(keys,values)
        try
            var classProperty = charIDToTypeID('Prpr');
            var propNull = charIDToTypeID( 'null' );
            var classNull = charIDToTypeID( 'null' );
            var typeOrdinal = charIDToTypeID('Ordn');
            var enumTarget = charIDToTypeID('Trgt');
            var classDocument = charIDToTypeID('Dcmn');
            var classLayer = charIDToTypeID('Lyr ');
            var propProperty = stringIDToTypeID("property");
            var propGeneratorSettings = stringIDToTypeID("generatorSettings");
            var strMySettings = "xui";
            var keyTo = charIDToTypeID( 'T   ' );
            var actionSet = charIDToTypeID( "setd" );
            var actionGet = charIDToTypeID( "getd" );
            var theRef = new ActionReference();
            theRef.putProperty(classProperty, propGeneratorSettings );
            theRef.putEnumerated(classDocument, typeOrdinal, enumTarget);
            var getDescriptor = new ActionDescriptor();
            getDescriptor.putReference(propNull,theRef);
            getDescriptor.putString(propProperty, strMySettings);
            var actionResult = executeAction( actionGet, getDescriptor, DialogModes.NO );
            var mySettingsDesc = actionResult.getObjectValue(propGeneratorSettings);
            if (keys.indexOf(",") > 0)
                keys = keys.split(',');
                values = values.split(',');
            else
                keys = [keys];
                values = [values];
            for (var x =0; x < keys.length; x ++)
                var key = keys[x];
                var value = values[x];
                var propMyStringProperty = stringIDToTypeID(key);
                mySettingsDesc.putString(propMyStringProperty,value);
            var setDescriptor = new ActionDescriptor();
            setDescriptor.putReference(propNull,theRef);
            setDescriptor.putObject(keyTo,classNull,mySettingsDesc);
            setDescriptor.putString(propProperty, strMySettings);
            executeAction( actionSet, setDescriptor, DialogModes.NO );
            return true;
        catch (e)
            var exception = {};
            exception.target = "setDocumentdata";
            exception.message = e.toString();
            return JSON.stringify(exception);
    getDocumentData: function(key)
        try
           var classProperty = charIDToTypeID('Prpr');
            var propNull = charIDToTypeID( 'null' );
            var classNull = charIDToTypeID( 'null' );
            var typeOrdinal = charIDToTypeID('Ordn');
            var enumTarget = charIDToTypeID('Trgt');
            var classDocument = charIDToTypeID('Dcmn');
            var classLayer = charIDToTypeID('Lyr ');
            var propProperty = stringIDToTypeID("property");
            var propGeneratorSettings = stringIDToTypeID("generatorSettings");
            var strMySettings = "xui"; //unique name for your settings/plugin
            var propMyStringProperty = stringIDToTypeID(key); //unique name for the setting
            var actionGet = charIDToTypeID( "getd" );
            var theRef = new ActionReference();
            theRef.putProperty(classProperty, propGeneratorSettings );
            theRef.putEnumerated(classDocument, typeOrdinal, enumTarget);
            var getDescriptor = new ActionDescriptor();
            getDescriptor.putReference(propNull,theRef);
            getDescriptor.putString(propProperty, strMySettings);
            var actionResult = executeAction( actionGet, getDescriptor, DialogModes.NO );
            var mySettingsDesc = actionResult.getObjectValue(propGeneratorSettings);
            return mySettingsDesc.getString(propMyStringProperty);
        catch (e)
            var exception = {};
            exception.target = "getDocumentData";
            exception.message = e.toString();
            return JSON.stringify(exception);