I've tried to index it like this:
   body: {
            name: form.value.name,
            title: form.value.title,
            description: form.value.description,
            published: new Date().toLocaleString(),
            stash: {
              "title": this.alternativeFields.value,
              "type": "object",
              "dynamic": true
            }
          }
Basically this.alternativeFields.value is an array that contains, for example:
["field1", "field2", "field3"]
And for every position of that array I want to create a field in the elastic document.
Is there a way to do that?