Incrementing a string field count in Kibana

In the below query likeCount is a string field, but I need to do a increment operation on it, with the below query, it is doing a concatenation operation instead of increment.

POST /posts/_update/<id>
{
  "script" : {
    "source": "ctx._source.likeCount++"
  }
}

It is working with below code Integer.toString worked.

POST /posts/_update/<id>
{
  "script": {
    "source": "ctx._source.likeCount = Integer.toString(Integer.parseInt(ctx._source.likeCount)+1);",
    "lang": "painless"
  }
}

Making it dynamic

POST /posts/_update/<id>
{
  "script": {
    "source": "ctx._source.likeCount = Integer.toString(Integer.parseInt(ctx._source.likeCount)+params.newValue);",
    "lang": "painless",
    "params" : {
      "newValue" : 1
    }
  }
}