Convert an array of objects to a single object

Index records by a key field.

JavaScript Version 1.0.0 · MIT · .md

function toObject({ values, key }) { return Object.fromEntries(values.map(item => [item[key], item])); }

Input & expected output

{
  "values": [
    {
      "id": "[email protected]",
      "status": "delivered"
    },
    {
      "id": "[email protected]",
      "status": "deferred"
    }
  ],
  "key": "id"
}

{
  "[email protected]": {
    "id": "[email protected]",
    "status": "delivered"
  },
  "[email protected]": {
    "id": "[email protected]",
    "status": "deferred"
  }
}

The edge case

{
  "values": [
    {
      "id": "a",
      "n": 1
    },
    {
      "id": "a",
      "n": 2
    }
  ],
  "key": "id"
}

{
  "a": {
    "id": "a",
    "n": 2
  }
}

Know the limits

• A repeated key keeps the last record, as the edge case shows.
• Uses the Object.fromEntries variant; the spread variant copies the accumulator on every item.

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

• Clone an array — Create a new array without copying the objects inside it.
• Remove duplicate values — Keep the first occurrence of each value, in its original order.
• Flatten a nested array — Turn a nested array into one sequence of values.