Filter for logged in user

I am creating a custom chart where logged-in users would be able to see the projects assigned to them. How do I create a filter for logged-in users? Any help is appreciated.
Thanks.

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In the projects.json file of Erpnext, they have mentioned this code for creating a shortcut to show assigned tasks to logged in users. I am not sure how to use the variable frappe.session.user in Erpnext UI?

 {
   "color": "Blue",
   "format": "{} Assigned",
   "label": "Task",
   "link_to": "Task",
   "stats_filter": "{\n    \"_assign\": [\"like\", '%' + frappe.session.user + '%'],\n    \"status\": \"Open\"\n}",
   "type": "DocType"
  }