Photoshop Scripting Artboard Size Values

ScriptingListener changing artboard size via Properties panel resizes from the fixed upper left... Resizing using the artboard tool (v) is "interactive"...

Combining the code from @Chuck Uebele with some further code:

#target photoshop 

var doc = activeDocument;
var aLayer = doc.activeLayer;
var ab = artboard_rectangle(aLayer);
var aW = ab[2]-ab[0];
var aH = ab[3] - ab[1];

//////////

// Add 100px to current artboard width & height
var aWresize = aW + 100;
var aHresize = aH + 100;

//////////

resizeArtboard(0, 0, aHresize, aWresize, "", 255, 255, 255, 1);

//////////

function artboard_rectangle(layer)
    {
    try {        
        var r    = new ActionReference();    
        r.putProperty(stringIDToTypeID("property"), stringIDToTypeID("artboard"));
        if (layer) r.putIdentifier(stringIDToTypeID("layer"), layer.id);
        else       r.putEnumerated(stringIDToTypeID("layer"), stringIDToTypeID("ordinal"), stringIDToTypeID("targetEnum"));
        var d = executeActionGet(r).getObjectValue(stringIDToTypeID("artboard")).getObjectValue(stringIDToTypeID("artboardRect"));
        var bounds = new Array();
        bounds[0] = d.getUnitDoubleValue(stringIDToTypeID("left"));
        bounds[1] = d.getUnitDoubleValue(stringIDToTypeID("top")); 
        bounds[2] = d.getUnitDoubleValue(stringIDToTypeID("right"));
        bounds[3] = d.getUnitDoubleValue(stringIDToTypeID("bottom"));                                

        return bounds;
        }
    catch(e) { alert(e); }
}

//////////

function resizeArtboard(top, left, bottom, right, artboardPresetName, red, grain, blue, artboardBackgroundType) {
	var s2t = function (s) {
		return app.stringIDToTypeID(s);
	};
	var descriptor = new ActionDescriptor();
	var descriptor2 = new ActionDescriptor();
	var descriptor3 = new ActionDescriptor();
	var descriptor4 = new ActionDescriptor();
	var list = new ActionList();
	var reference = new ActionReference();
	reference.putEnumerated( s2t( "layer" ), s2t( "ordinal" ), s2t( "targetEnum" ));
	descriptor.putReference( s2t( "null" ), reference );
	descriptor3.putDouble( s2t( "top" ), top );
	descriptor3.putDouble( s2t( "left" ), left );
	descriptor3.putDouble( s2t( "bottom" ), bottom );
	descriptor3.putDouble( s2t( "right" ), right );
	descriptor2.putObject( s2t( "artboardRect" ), s2t( "classFloatRect" ), descriptor3 );
	descriptor2.putList( s2t( "guideIDs" ), list );
	descriptor2.putString( s2t( "artboardPresetName" ), artboardPresetName );
	descriptor4.putDouble( s2t( "red" ), red );
	descriptor4.putDouble( s2t( "grain" ), grain );
	descriptor4.putDouble( s2t( "blue" ), blue );
	descriptor2.putObject( s2t( "color" ), s2t( "RGBColor" ), descriptor4 );
	descriptor2.putInteger( s2t( "artboardBackgroundType" ), artboardBackgroundType );
	descriptor.putObject( s2t( "artboard" ), s2t( "artboard" ), descriptor2 );
	executeAction( s2t( "editArtboardEvent" ), descriptor, DialogModes.NO );
}