D365 CRM如何使用queryselectorall()访问子网格单元格DOM

我的客户需要这个功能,我是CRM定制的新手,我主要做后端插件自定义操作和自定义api。以下所有3个代码始终返回null。我做错了什么。

function myGridClickHandler(executionContext) {

let formContext = executionContext.getFormContext(); 
let gridContext = formContext.getControl("Document_Barcodes2"); 
let grid = gridContext.getGrid();
let myContactsGridOnloadFunction = function() {
    console.log("Document_Barcodes2 Subgrid OnLoad event occurred");

  
   let elements = window.parent.document.querySelectorAll("div.ag-cell"); 
   let elements2 = document.querySelectorAll("div.ag-cell"); 
   let elements3=document.querySelectorAll('.ag-cell[col-id="ct_preview"]');
     debugger;  
    
    }
  gridContext.addOnLoad(myContactsGridOnloadFunction);



         
}

The page and subgrid, it's the second one

The id,class... of the element i need to select