Javascript arrays: Can you have both keys and values?

I used an ethers.providers.getLogs() function on an arbitrary transaction in javascript. I got the following result as one of the parameters.

There seems to be key-pair values in this array (denoted by the brackets []), which doesn't make sense. This makes me think this as an object. But that can't be the case as well because there are singular keys without pairs.

Can someone explain what's going on here?

[
  '0xd2ab1089822171b728a5694b79acf292f6b59ff8c548d2a2e71f6c5ff7025f0f',
  '0xcd63cB2374e49f88083d79D5f7891be5734cdc68',
  '0x0000000000000000000000000000000000000000',
  BigNumber { _hex: '0x38', _isBigNumber: true },
  true,
  BigNumber { _hex: '0xc817c38c6ddc', _isBigNumber: true },
  BigNumber { _hex: '0x023c74', _isBigNumber: true },
  userOpHash: '0xd2ab1089822171b728a5694b79acf292f6b59ff8c548d2a2e71f6c5ff7025f0f',
  sender: '0xcd63cB2374e49f88083d79D5f7891be5734cdc68',
  paymaster: '0x0000000000000000000000000000000000000000',
  nonce: BigNumber { _hex: '0x38', _isBigNumber: true },
  success: true,
  actualGasCost: BigNumber { _hex: '0xc817c38c6ddc', _isBigNumber: true },
  actualGasUsed: BigNumber { _hex: '0x023c74', _isBigNumber: true }
]

This is a text representation of an array that also has non-integer-keyed properties, used by e.g. Node.js’s console.log (with the default %O format)/util.inspect.

As @ThisGuy noted in the comments,

> seems like the data is there twice. once as raw, unlabeled data. then a second set, using key and value

The creator of the library you’re using might be doing that for backwards compatibility, e.g. if the function originally returned an array but then it was decided that named properties were a better choice.

<!-- begin snippet: js hide: false console: true babel: false -->

<!-- language: lang-js -->

class BigNumber {
  constructor(hex) {
    this._hex = hex;
    this._isBigNumber = true;
  }
}

const exact = [
  '0xd2ab1089822171b728a5694b79acf292f6b59ff8c548d2a2e71f6c5ff7025f0f',
  '0xcd63cB2374e49f88083d79D5f7891be5734cdc68',
  '0x0000000000000000000000000000000000000000',
  new BigNumber('0x38'),
  true,
  new BigNumber('0xc817c38c6ddc'),
  new BigNumber('0x023c74'),
];

Object.assign(exact, {
  userOpHash: '0xd2ab1089822171b728a5694b79acf292f6b59ff8c548d2a2e71f6c5ff7025f0f',
  sender: '0xcd63cB2374e49f88083d79D5f7891be5734cdc68',
  paymaster: '0x0000000000000000000000000000000000000000',
  nonce: new BigNumber('0x38'),
  success: true,
  actualGasCost: new BigNumber('0xc817c38c6ddc'),
  actualGasUsed: new BigNumber('0x023c74'),
});

document.getElementById('formatted').textContent = util.inspect(exact);

<!-- language: lang-html -->

<script src="https://unpkg.com/node-inspect-extracted/dist/inspect.js"></script>
<pre id="formatted"></pre>

<!-- end snippet -->