npm and error messages

node_modules/core-js/modules/_collection-to-json.js

@@ -0,0 +1,9 @@
+// https://github.com/DavidBruant/Map-Set.prototype.toJSON
+var classof = require('./_classof');
+var from = require('./_array-from-iterable');
+module.exports = function (NAME) {
+  return function toJSON() {
+    if (classof(this) != NAME) throw TypeError(NAME + "#toJSON isn't generic");
+    return from(this);
+  };
+};