Add timeline read markers API (#11762)

Fix #4093

app/javascript/mastodon/actions/markers.js

@@ -0,0 +1,30 @@
+export const submitMarkers = () => (dispatch, getState) => {
+  const accessToken = getState().getIn(['meta', 'access_token'], '');
+  const params      = {};
+
+  const lastHomeId         = getState().getIn(['timelines', 'home', 'items', 0]);
+  const lastNotificationId = getState().getIn(['notifications', 'items', 0, 'id']);
+
+  if (lastHomeId) {
+    params.home = {
+      last_read_id: lastHomeId,
+    };
+  }
+
+  if (lastNotificationId) {
+    params.notifications = {
+      last_read_id: lastNotificationId,
+    };
+  }
+
+  if (Object.keys(params).length === 0) {
+    return;
+  }
+
+  const client = new XMLHttpRequest();
+
+  client.open('POST', '/api/v1/markers', false);
+  client.setRequestHeader('Content-Type', 'application/json');
+  client.setRequestHeader('Authorization', `Bearer ${accessToken}`);
+  client.send(JSON.stringify(params));
+};