Add polyfill for String.prototype.includes

static/scripts/custom/polyfills.js

@@ -0,0 +1,15 @@
+// Polyfill from https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/includes
+if (!String.prototype.includes) {
+  String.prototype.includes = function(search, start) {
+    'use strict';
+    if (typeof start !== 'number') {
+      start = 0;
+    }
+
+    if (start + search.length > this.length) {
+      return false;
+    } else {
+      return this.indexOf(search, start) !== -1;
+    }
+  };
+}