cache last heartbeat list in memory

server/limit-array.js

@@ -0,0 +1,13 @@
+class LimitArray {
+    limit = 100;
+    array = [];
+
+    add(item) {
+        this.array.push(item);
+        if (this.array.length > this.limit) {
+            this.array.shift();
+        }
+    }
+}
+
+module.exports = LimitArray;