ElasticSearch: Append to array

add_to_array.js

const created_by = '12345566';
const script = 'if (ctx._source.raters == null) { ctx._source.raters = [] } \
if (ctx._source.raters.indexOf(params.created_by) == -1) {\
  ctx._source.raters.add(params)\
}';
return this.client.update({
  index: 'index',
  type: 'type',
  id: 'key',
  body: {
    script: {
      lang: 'painless',
      source: script,
      params: {
        created_by: created_by
      }
    }
  }
});