contenteditable attribute of a div hanging with document.execCommand and insertunorderedlist

[halloweenman]

Description

I'm writing a very basic WYSIWYG rich editor using contenteditable attribute of a div but experiencing issues with document.execCommand and executing the command insertunorderedlist. If you select and highlight the text you want to insert an unordered list and click insert button then it either fails to work correctly using Chrome (latest version) or if using Safari (latest version High Sierra), just hangs. If you try this outside of webcomponents / Polymer (plain old html and javascript) it works fine. Here's the code:

<link rel="import" href="../../bower_components/polymer/polymer-element.html">

<dom-module id="polymerbasic-app">
  <template>
    <style>
      :host {
        display: block;
      }
    </style>

    <button on-click="_insertunorderedlist" type="button">Insert Unordered List</button>

    <div id="textBox" contenteditable="true">
      Bullet One
      <br> Bullet Two
      <br> Bullet Three
    </div>
  </template>

  <script>
    /**
     * @customElement
     * @polymer
     */
    class PolymerbasicApp extends Polymer.Element {
      static get is() { return 'polymerbasic-app'; }
      static get properties() {
        return {
          prop1: {
            type: String,
            value: 'polymerbasic-app'
          }
        };

      }
      _insertunorderedlist() {
        document.execCommand("insertunorderedlist", false, null); this.$.textBox.focus();
      }

    }

    window.customElements.define(PolymerbasicApp.is, PolymerbasicApp);
  </script>
</dom-module>

Steps to Reproduce

Select and highlight Bullet One, Bullet Two, and Bullet Three text and click on insert button using Safari or other browser.

Expected Results

html Unordered list.

Actual Results

Hangs, or does not behave correctly.

Browsers Affected

• [ x] Chrome
• [ x] Firefox
• [ x] Edge
• [ x] Safari 9
• [ x] Safari 8
• [ x] IE 11

Versions

• Polymer: v1.11.3
• webcomponents: v1.1.0

[TimvdLippe]

Closing this per Polymer/polymer#5158 (comment)