opal/corelib/runtime.js in opal-1.7.3 vs opal/corelib/runtime.js in opal-1.7.4

@@ -1861,12 +1861,17 @@
       Object.assign(block, blockopts);
     }
   }
 
   // Optimization for a costly operation of prepending '$' to method names
-  var jsid_cache = {}
+  var jsid_cache = new Map();
   function $jsid(name) {
-    return jsid_cache[name] || (jsid_cache[name] = '$' + name);
+    var jsid = jsid_cache.get(name);
+    if (!jsid) {
+      jsid = '$' + name;
+      jsid_cache.set(name, jsid);
+    }
+    return jsid;
   }
   Opal.jsid = $jsid;
 
   // Calls passed method on a ruby object with arguments and block:
   //