Syntax question (capitalize first letter)

Working with Data
,
4

The properties firstName and lastName are inside a profile object so don’t need to do any $reduce or $map operators, look at the below pipeline, it will cut the first character from the string and make it upper case and concat with next characters,

db.hej.aggregate([
  {
    $set: {
      "profile.firstName": {
        $concat: [
          { $toUpper: { $substr: ["$profile.firstName", 0, 1] } },
          { $substr: ["$profile.firstName", 1, { $strLenCP: "$profile.firstName" }] }
        ]
      },
      "profile.lastName": {
        $concat: [
          { $toUpper: { $substr: ["$profile.lastName", 0, 1] } },
          { $substr: ["$profile.lastName", 1, { $strLenCP: "$profile.lastName" }] }
        ]
      }
    }
  }
])