An array subclass that enforces a maxLength

The maxLength is enforced by removing elements from the head of the
list.

ui/app/utils/classes/rolling-array.js

@@ -0,0 +1,45 @@
+// An array with a max length.
+//
+// When max length is surpassed, items are removed from
+// the front of the array.
+
+// Using Classes to extend Array is unsupported in Babel so this less
+// ideal approach is taken: https://babeljs.io/docs/en/caveats#classes
+export default function RollingArray(maxLength, ...items) {
+  const array = new Array(...items);
+  array.maxLength = maxLength;
+
+  // Capture the originals of each array method, but
+  // associate them with the array to prevent closures.
+  array._push = array.push;
+  array._splice = array.splice;
+  array._unshift = array.unshift;
+
+  array.push = function(...items) {
+    const returnValue = this._push(...items);
+
+    const surplus = this.length - this.maxLength;
+    if (surplus > 0) {
+      this.splice(0, surplus);
+    }
+
+    return returnValue;
+  };
+
+  array.splice = function(...args) {
+    const returnValue = this._splice(...args);
+
+    const surplus = this.length - this.maxLength;
+    if (surplus > 0) {
+      this._splice(0, surplus);
+    }
+
+    return returnValue;
+  };
+
+  array.unshift = function() {
+    throw new Error('Cannot unshift onto a RollingArray');
+  };
+
+  return array;
+}