Issue grouping objects together using a script

Sorry for spamming this thread but I believe that I finally found a solution to my issue. I wanted to share it in case someone else has a similar problem.

I began tinking about the process when you're not scripting. You always select the items you want to apply an effect to. I therefore used the loop from before to make three selections, I then group the selections one by one and ultimately I apply the warp effect to these groupItem objects.

Here is the code:

// Open a file using these preferences
var fileRef = new File(myPath + "mug_canvas_3.pdf");

if (fileRef != null) {
  var docRef = open(fileRef, DocumentColorSpace.RGB, );
}

var docH = docRef.height;
var docW = docRef.width;
var ref1 = docH/3, ref2 = 2*docH/3;

var numGroupItems = docRef.groupItems.length;
//Print some relevant information about the document
$.writeln('docH: ' + docH + " docW: " + docW
          + " ref1: " + ref1 + " ref2: " + ref2
          + " num group items: " + numGroupItems);

var i, j, docGI = docRef.groupItems;
//Document is divided into three equally large areas which contain designs
//there might not be a design there, so this variable checks if there is
var designCheck = [];

//Loop three times for the three areas
for(j = 0; j < 3; j++) {
  designCheck[j] = false;
  docRef.selection = null;
  //Loop through all groupItem elements in the document
  for(i = 0; i < numGroupItems; i++) {
    var gi = docGI[i];
    //For the first area, check if groupItem contained within first third
    if(gi.controlBounds[3] < (ref1 - 10) && j == 0) {
      gi.selected = true;
      designCheck[0] = true;
      //For the second area, check if groupItem contained within second third
    } else if(gi.controlBounds[3] < (ref2 - 10) && gi.controlBounds[3] > (ref1 + 10) && j == 1) {
      gi.selected = true;
      designCheck[1] = true;
      //For the last area, check if groupItem contained within third third
    } else if(j == 2 && gi.controlBounds[3] > (ref2 + 10)) {
      gi.selected = true;
      designCheck[2] = true;
    }
  }
  //Group all the items selected to create one groupItem
  app.executeMenuCommand("group");  
}

app.redraw();

$.writeln('Num layers: ' + docRef.layers.length);
$.writeln('groups in layer: ' + docRef.layers[0].groupItems.length);

//Apply warp effect to all the groupItem elements in the layer
for(j = 0; j < docRef.layers[0].groupItems.length; j++) {
  if(designCheck[j] === true) {
    var placed = docRef.layers[0].groupItems[j];
    var effectStr = '<LiveEffect name="Adobe Deform"><Dict data="R DeformValue -0.115 R DeformVert 0 B Rotate 0 I DeformStyle 1 R DeformHoriz 0 "/></LiveEffect>';
    placed.applyEffect(effectStr);
    //This applies an envelope effect to the warped object
    //Useful if you want specific dimensions
    app.redraw();
    app.executeMenuCommand('expandStyle');
  }
}  

Thank you again @Silly-V and @femkeblanco for the help. If you have any insights or comments on the solution please let me know 🙂