{{ items | join('|') }}

{
  "items": [1, 2, 3]
}

{{ items | join }}

{
  "items": [1, 2, 3]
}

{{ items | join(', ', 'name') }}

{
  "items": [
    { "name": "alpha" },
    { "name": "bravo" },
    { "name": "charlie" }
  ]
}