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const editor = grapesjs.init({
  container: '#gjs',
  fromElement: true,
  height: '100%',
  storageManager: false,
  noticeOnUnload: false,
  selectorManager: {
    custom: true,
    componentFirst: true,
  },
});

// Load the Vue app
const sm = editor.Selectors;
const app = new Vue({
  el: '.selectors-wrp',
  data: { selectors: [], states: [], state: null, targets: '' },
  mounted() {
    editor.on('selector:custom', this.handleCustom);
  },
  destroyed() {
    editor.off('selector:custom', this.handleCustom);
  },
  methods: {
    handleCustom(props) {
      if (props.container) {
        props.container.appendChild(this.$el);
      }
      this.selectors = sm.getSelected();
      this.states = sm.getStates();
      this.state = sm.getState();
      this.targets = sm.getSelectedTargets()
      	.map(target => target.getSelectorsString()).join(', ');
    },
    changeState(ev) {
      sm.setState(ev.target.value);
    },
    remove(selector) {
      sm.removeSelected(selector);
    },
    addNew() {
      const len = sm.getAll().length + 1;
      sm.addSelected({ name: `new-${len}`, label: `New ${len}` });
    },
  }
});

<div id="gjs">
  <div style="padding: 25px">Custom Selector Manager</div>
  <div class="class-a">Element A</div>
  <div class="class-a class-b">Element A-B</div>
  <div class="class-a class-b class-c">Element A-B-C</div>
  <style>
    .class-a { color: red }
    .class-b { color: green }
    .class-c { color: blue }
  </style>
</div>

<div style="display: none;">
  <!-- Vue app  -->
  <div class="selectors-wrp">
    <div class="selectors-head">
      <div class="selectors-title">Classes</div>
      <div class="selectors-states">
        <select @change="changeState" :value="state">
          <option value="">- State -</option>
          <option v-for="state in states" :key="state.getName()">
            {{ state.getLabel() }}
          </option>
        </select>
      </div>
    </div>
    <div class="selectors">
      <div class="selector-add" @click="addNew">&plus;</div>
      <div v-for="sel in selectors" :key="sel.toString()" class="selector">
        <div class="selector-name">{{ sel.getLabel() }}</div>
        <div class="selector-rm" @click="remove(sel)">&Cross;</div>
      </div>
    </div>
    <div class="selectors-targets">
      Selected: {{ targets }}
    </div>
  </div>
</div>

body, html {
  margin: 0;
  height: 100%;
}

.selectors-wrp {
  padding: 10px 5px;
}
.selectors-head {
  display: flex;
  align-items: center;
}
.selectors-title {
  flex-grow: 1;
  text-align: left;
}
.selectors {
  display: flex;
  flex-wrap: wrap;
  background-color: rgb(0 0 0 / 15%);
  padding: 3px 5px;
  border-radius: 3px;
  margin: 10px 0;
  gap: 5px;
}
.selector, .selector-add {
  display: flex;
  gap: 3px;
  background-color: #8f4a79;
  color: white;
  padding: 2px 5px 3px;
  border-radius: 3px;
  align-items: center;
  white-space: nowrap;
}
.selector-add {
  font-size: 1rem;
  padding: 2px 8px 3px;
  background-color: rgb(255 255 255 / 25%);
  cursor: pointer;
}
.selector-rm {
  font-size: 1rem;
  cursor: pointer;
}
.selectors-targets {
  text-align: left;
}