Getting error converting dart2js on polymer project


Unsupported operation: Can’t use ownerName in reflection because it is not included in a @MirrorsUsed annotation.

ownerName is just an published attribute on the polymer element. I understand there are a few things out there (on web, not on here) like this but none have a solid answer…

I also get this below it:

NoSuchMethodError : method not found: ‘Symbol(“title”)’

Anyone got any ideas. Been wrestling with this for 3 hours and ready to dump polymer. Though It was fun in dartium, if it cannot convert to JS I see no real use in it.

import 'package:polymer/polymer.dart';
import 'package:google_postendpoint_v1_api/postendpoint_v1_api_browser.dart';
import 'package:google_postendpoint_v1_api/postendpoint_v1_api_client.dart';
import 'dart:math';
//import 'package:intl/intl.dart';

 * A Polymer post element.
class SoberSky extends PolymerElement {
  @published int count = 0;
  @published String ownerName = "Casey";
  @published int ownerId = 888;
  @published int postId = 333;
  @published String content = "yo ho ho, and a bottle of rumsky!";
  @published String postContent = "This is an example of post content";

  @published int getOwnerId = 333;
  @published CollectionResponse_Comment listComment;
  @published CollectionResponse_Post listPost;
  @published String listCommentHTML;
  @published Post currentPost;
  @published bool yes = false;
  Postendpoint endpoint = new Postendpoint();
  var rng = new Random();

  var commentList;

  SoberSky.created() : super.created() {
    endpoint.rootUrl = "http://localhost:8888/"; // set the root URL

  void getListComment([int tempPostId]) {
    if (tempPostId == null) {
      tempPostId = postId;
    endpoint.listComment( tempPostId ).then((CollectionResponse_Comment commentCollection){
          this.listComment = commentCollection;
    }).catchError((e) => handleError(e));

  void getPost() {
    endpoint.getPost( postId ).then((Post loadedMessage) {
      currentPost = loadedMessage; 
    }).catchError((e) => handleError(e));

  void submitComment() {
    int id = rng.nextInt(1000);
    Comment comment = new Comment.fromJson({}); = id;
    comment.content = content;
    comment.postId = postId;
    comment.ownerName = ownerName;
    comment.ownerId = ownerId;

    endpoint.insertComment( comment ).then((Comment savedComment) => endpoint.getComment(id)).
      then((Comment loadedMessage) {
      }).catchError((e) => handleError(e));  

  void submitPost(){
    postId = rng.nextInt(1000);
    Post post = new Post.fromJson({});
    post.key = postId;
    post.ownerName = ownerName;
    post.ownerId = ownerId;
    post.title = postContent;

    endpoint.insertPost( post ).then((Post savedPost) => endpoint.getPost(postId)).
    then((Post loadedMessage) {
    }).catchError((e) => handleError(e));

  void handleError(Error e) {
    print("We had an error: ");

  void attached() {

The HTML Polymer element

<polymer-element name="click-counter" attributes="count">
    <form action="javascript:void(0);" >
      <div class="entry">
        <label>Enter Post:</label>
        <input id="subject" type="text" value="{{postContent}}" size="45" maxlength="255">
        <button on-click="{{submitPost}}" class="btn btn-success" >Submit Post</button>    <br>

    <div class="post">  
      <h3>{{ currentPost.ownerName }}</h3>
      <p>{{ currentPost.title }}</p>
      <p>This is the postId: {{ currentPost.key }}</p>
  <p class="timestamp">{{ currentPost.uploadTime }}</p>
  <template repeat="{{comment in listComment.items}}">
    <div class="comment">
      <h3>{{ comment.ownerName }}</h3>
      <p>{{ comment.content }}</p>
      <p>This is the commentId: {{ }}</p>
      <p class="timestamp">{{ comment.formatDate }}</p>
      <form action="javascript:void(0);">
        <label>Enter Comment:</label>
        <input id="subject" type="text" value="{{content}}" size="45" maxlength="255">
            <button on-click="{{submitComment}}" class="btn btn-success">Submit Comment</button>    <br>
  <script type="application/dart" src="clickcounter.dart"></script>  


I have not yet seen your Unsupported operation message. Maybe some recent change. Your NoSuchMethodError is common when a property of a class is only referenced by a polymer expression (HTML) because tree-shaking drops all code that is not referenced and polymer expressions are not evaluated for this yet. The @MirrorsUsed annotation helps bridging this gap.

The problem is in your Post class because it’s properties are only referenced in polymer expressions

<div class="post">  
  <h3>{{ currentPost.ownerName }}</h3>
  <p>{{ currentPost.title }}</p>
  <p>This is the postId: {{ currentPost.key }}</p>
  <p class="timestamp">{{ currentPost.uploadTime }}</p>

To get your view updated when the properties in your currentPost change you should make your Post class like

class Post extends Object with Observable {
  @observable String ownerName;
  @observable String title;

If you have an annotation like @reflectable, @published, or @observable you don’t need @MirrorsUsed.

Answered By – Günter Zöchbauer

Answer Checked By – Dawn Plyler (FlutterFixes Volunteer)

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