Accessing child table row on load

I am trying to access the rows of the child table on load and hide some of it dynamically in doctype in js file. However, when I try to access it, the code of accessing the rows is being executed before the load finishes so therefore, I get undefined. How can I access the rows after the load but still under the onload function ?

On client side use onload_post_render but you will need to refresh the fields with frm.refresh_fields

Thank you so much this helped a lot. If you don’t mind me bothering you again, i now get the individual rows but when I set the hidden field as true, the value gets updated but the rows still remain shown. I did the frm_refresh_fields as well but to no help. Any help would be greatly appreciated