Javascript method to set the default value in search grid?

We need to limit the search results of "Document" item for certain identity. 

The default value of  "Classification" should be prefilled to  "General" and should be unchangeable by the user.

I was thinking if I can get the current identity of the user and then call a function that would prefill the "Classification" to "General" and make it uneditable.


I have a code for finding the identity of the user. I need to know how to target the "Classification" field of "Document" item type in the search grid view




thanks!