ck-editor-wrapper-test/src/components/CustomImageClassPlugin.js

A VueJS CkEditor wrapper

import { Plugin } from 'ckeditor5'

export default class CustomImageClassPlugin extends Plugin {
  init() {
    const editor = this.editor
    editor.model.document.on('change:data', () => {
      const viewDocument = editor.editing.view.document
      const viewRoot = viewDocument.getRoot()
      editor.editing.view.change(viewWriter => {
        if (viewRoot) {
          for (const node of viewRoot.getChildren()) {
            if (node) {
              const testElement = node
              if (testElement.name === 'figure' && testElement.hasClass('image')) {
                if (!testElement.hasClass('etp-ckeditor5-figure')) {
                  console.log('image custom class added')
                  viewWriter.addClass('etp-ckeditor5-figure', testElement)
                }
              }
            }
          }
        }
      })
    })
  }
}