JS - Center Selection to Artboard / New Document with certain Artboard size

Question

TL;DR:
how do I center my current selection to the artboard?
just like hitting the "horizontal align-center" and "vertical align-center" buttons.
Hi,
I've been searching for the last two hours and before my head hits the keyboard I wanted to ask you for help.
What I'm struggling with:
in my init function i create a new document and then copy all layers from the previous document step by step to the new document and then save it as SVG.
// Init
(function(){
          destination = Folder.selectDialog('Select folder for SVG files.', docPath);
          if (!destination){return;}
          holderDoc = app.documents.add();
          stepThroughAndExportLayers(docRef.layers);
my problem is that holderDoc = app.documents.add(); always creates a document that is not the same size as my initial document where the layers get copied from.
so I want the exact same artboard size as in my initial document.
I'm fine with either doing it as fixed values or taking directly the values of the inital doc.
i tried this in the segment where I create the new document:
// Init
(function(){
  destination = Folder.selectDialog('Select folder for SVG files.', docPath);
  if (!destination){return;}
  holderDoc = app.documents.add();
  holderDoc.artboards[0].artboardRect = [0,0,128,128];
  stepThroughAndExportLayers(docRef.layers);
and get this error message:
"Error 1200: an Illustrator error occured: 1346458189 ('PARM')
Line: 83
-> holderDoc.artboards[0].artboardRect = [0,0,128,128];"
which from what I've read on the web means that illustrator doesnt know what document to pick. but i have called it directly. so what could be the issue?
to clearify: I do not want to fit the artboard to the images/layer. the artboard should always have a certain size. (for me 128px by 128px)
I would highly appreciate you helping me with either fixing my approach or propose a completely new one.
Thanks so much in advance.
// edit: workaround
(function(){
          destination = Folder.selectDialog('Select folder for SVG files.', docPath);
          if (!destination){return;}
          var activeArtboard = app.activeDocument.artboards[app.activeDocument.artboards.getActiveArtboardIndex()];
          var ABRect = activeArtboard.artboardRect;
          holderDoc = app.documents.add();
          holderDoc.artboards.add(ABRect);
          holderDoc.artboards.remove(0);
          holderDoc.artboards.setActiveArtboardIndex(0);
          //stepThroughAndExportLayers(docRef.layers);
i now added a new artboard to the new document with the same size as the artboard on the initial document.
i remove the predefined artboard on the new doc and set the new artboard as active.
BUT!
the artboard is now not centered into the window. which lets illustrator place my image with ctrl+c -> ctrl+v somewhere outside the artboard.
i now need to align my selection to the center of the artboard. but i cant find any reference on how to center a selection to the artboard.

Answer 1

yes of course. i never modify the author's comments in original scripts.
but I wont post the script anywhere when it doesnt work anyway haha.
this is what I've done now:
// Init
(function(){
          destination = Folder.selectDialog('Select folder for SVG files.', docPath);
          if (!destination){return;}
          var activeArtboard = app.activeDocument.artboards[app.activeDocument.artboards.getActiveArtboardIndex()];
          var ABRect = activeArtboard.artboardRect;
          // create new document with same artboard as original
          holderDoc = app.documents.add(DocumentColorSpace.RGB, new UnitValue ((Math.abs(ABRect[0]-ABRect[2])), "px"), new UnitValue ((Math.abs(ABRect[0]-ABRect[2])), "px"));
          stepThroughAndExportLayers(docRef.layers);
in order to create the new document with the same dimensions as my orignal doc, I first read the artboardRect dimensions of the current artboard and then create the document with those values passed as parameters. the calculation is to get the real width since artboardRect gives you left,top,right,bottom values and not just height and width.
this only works for square formats though. to make it properly you'd have to change the second "new UnitValue" to use the top and bottom values of artboardRect but I currently dont need to do so.
* Layers to SVG - layers_export.jsx
* @version 0.1
* Improved PageItem selection, which fixed centering
* @author Anton Ball
* Exports all layers to SVG Files
* I didn't want every layer in the SVG file so it first creates a new document
* and one by one copies each layer to that new document while exporting it out
* as an SVG.
* TODO:
* 1. More of an interface wouldn't hurt. Prefix option and progress bar of some description.
// Variables
var docRef = app.activeDocument,
          docPath = docRef.path,
          ignoreHidden = true,
          svgExportOptions = (function(){
                    var options = new ExportOptionsSVG();
                    options.fontSubsetting = SVGFontSubsetting.GLYPHSUSED;
                    options.embedRasterImages = true;
                    options.fontType = SVGFontType.OUTLINEFONT;
                    return options;
          destination, holderDoc;
// Functions
var stepThroughAndExportLayers = function(layers){
          var layer,
                    numLayers = layers.length;
          for (var i = 0; i < numLayers; i += 1){
                    layer = layers[i];
                    if (ignoreHidden && !layer.visible){continue;}
                    copyLayerTo(layer, holderDoc);
                    // Resize the artboard to the object
                    selectAll(holderDoc);
                    exportAsSVG(validateLayerName(layer.name, '-'), holderDoc);
                    // Remove everything
                    holderDoc.activeLayer.pageItems.removeAll();
          holderDoc.close(SaveOptions.DONOTSAVECHANGES);
// Copies the layer to the doc
copyLayerTo = function(layer, doc){
          var pageItem,
                    numPageItems = layer.pageItems.length;
          for (var i = 0; i < numPageItems; i++){
                    pageItem = layer.pageItems[i];
                    pageItem.duplicate(holderDoc.activeLayer, ElementPlacement.PLACEATEND);
// Selects all PageItems in the doc
selectAll = function(doc){
          var pageItems = doc.pageItems,
                    numPageItems = doc.pageItems.length;
          for (var i = 0; i < numPageItems; i += 1){
                    pageItems[i].selected = true;
// Exports the doc to the destination saving it as name
exportAsSVG = function(name, doc){
          var file = new File(destination + '/' + name + '.svg');
          holderDoc.exportFile(file, ExportType.SVG, svgExportOptions);
// Makes sure the name is lowercase and no spaces
validateLayerName = function(value, separator){
          separator = separator || '_';
          //return value.toLowerCase().replace(/\s/, separator);
          return value.replace(/\s/, separator);
// Init
(function(){
          destination = Folder.selectDialog('Select folder for SVG files.', docPath);
          if (!destination){return;}
          var activeArtboard = app.activeDocument.artboards[app.activeDocument.artboards.getActiveArtboardIndex()];
          var ABRect = activeArtboard.artboardRect;
          // create new document with same artboard as original
          holderDoc = app.documents.add(DocumentColorSpace.RGB, new UnitValue ((Math.abs(ABRect[0]-ABRect[2])), "px"), new UnitValue ((Math.abs(ABRect[0]-ABRect[2])), "px"));
          stepThroughAndExportLayers(docRef.layers);