CM6 linting and error notifications/highlighting

v6
5

You should be able to use the one included in the language package: codemirror/lang-json.

import { linter } from '@codemirror/lint'
import { json, jsonParseLinter } '@codemirror/lang-json'

const linterExtension = linter(jsonParseLinter())

const editor = new EditorView({
  state: EditorState.create({
    extensions: [json(), linterExtension]
  }),
  parent: document.body
})