How do I script a PNG24 file to have white opaque background

well you can do something like this ...though  i`m quite out of the subject on this one:

var doc = app.activeDocument;

var docRef = app.documents.add();

app.activeDocument = doc;

for(j = doc.pageItems.length - 1; j>=0; j--){

     //not quite sure if it gets as pageItem, pathItems inside CopoundPaths for example;

     if(doc.pageItems.parent.typename == "Layer") doc.pageItems.duplicate(docRef);

}

//(********* CODE CREDITS GO TO Muppet Mark ********)

var userHome = Folder("~").fsName.toString();

var fileRef = new File (userHome + '/Desktop/Marks_Star.png');

exportAsPNG24File(fileRef, 'Flat');

function exportAsPNG24File(saveFile, x) {

var exportType = ExportType.PNG24;

var png24Options = new ExportOptionsPNG24();

with (png24Options) {

switch(x) {

case 'Flat' :

transparency = false;

var bgMatte = new RGBColor();

bgMatte.red = 255; bgMatte.green = 255; bgMatte.blue = 255;

matte = true;

matteColor = bgMatte; break;

case 'Tran' :

matte = false;

transparency = true; break;

}

antiAliasing = true;

artBoardClipping = true;

horizontalScale = 100;

saveAsHTML = false;

verticalScale = 100;

}

docRef.exportFile(saveFile, exportType, png24Options);

}

hope itsomehow helps;

cheers;