REDCap: describe how to retrieve event_id

Author: kairstenfay

REDCap.md

@@ -1,5 +1,34 @@
+- [Enable DETs for a project](#enable-dets-for-a-project)
+- [Find event ID for an event name](#find-event-id-for-an-event-name)
+
 ## Enable DETs for a project
 
 Within the REDCap project, go to Project Setup.
 Find and click the Additional Customizations button.
 Scroll to the bottom of the modal, and find the Data Entry Trigger section.
+
+
+## Find event ID for an event name
+
+There is no official REDCap API for retrieving an event ID, but this event ID is required for generating deep links to specific instance of forms within REDCap.
+
+To find the event ID, you can look at the `event_id` param in the URL of a form from your target arm and event.
+If there are no forms for the arm or event you're targeting, then with a little hacking, you can retrieve the event ID in the following way:
+1. From the home page of your target REDCap project, under **Project Home and Design**, click on **Project Setup**.
+2. Then, under **Define your events and designate instruments for them**, click `Define my events`.
+3. In your browser console, run the following JavaScript snippet:
+    ```js
+    edit_links = document.querySelectorAll("a[onclick^=beginEdit]")
+    parse_onclick = a =>
+        a.getAttribute("onclick")
+    .match(/beginEdit\("(?<arm>\d+)","(?<event_id>\d+)"\)/)
+    .groups;
+    console.table(
+    Array.from(edit_links).map(a => ({
+        name: a.parentElement.parentElement.querySelector(".evt_name").textContent,
+        ...parse_onclick(a)
+    }))
+    )
+    ```
+The resulting table detials the `event_id` for each event defined in the current tab's arm.
+Click through the other tabs to see `event_ids` for other project arms.