Get unique objects from an array by key

Keep one record per key value, the last one seen.

JavaScript Version 1.0.0 · MIT · .md

function uniqueBy({ objects, key }) { return [...new Map(objects.map(item => [item[key], item])).values()]; }

Input & expected output

{
  "objects": [
    {
      "recipient": "[email protected]",
      "status": "deferred"
    },
    {
      "recipient": "[email protected]",
      "status": "delivered"
    },
    {
      "recipient": "[email protected]",
      "status": "delivered"
    }
  ],
  "key": "recipient"
}

[
  {
    "recipient": "[email protected]",
    "status": "delivered"
  },
  {
    "recipient": "[email protected]",
    "status": "delivered"
  }
]

The edge case

{
  "objects": [],
  "key": "id"
}

[]

Know the limits

• The last record per key wins, in the position of the first one — handy for keeping the latest state per recipient.

The function above is the implementation used by the lab. The lab validates JSON types and caps size before execution; include equivalent validation when accepting untrusted input in your application.

Keep exploring

• Pick properties from an object — Build a new object with only the requested own properties.
• Omit properties from an object — Keep the own enumerable fields that are not in a supplied list.
• Create an object from pairs of key and value — Turn [key, value] pairs into a plain object with Object.fromEntries.