curl --fail-with-body "$THORNODE_RPC_URL" \
  --header 'content-type: application/json' \
  --data '{
    "jsonrpc": "2.0",
    "id": 1,
    "method": "getSlotLeaders",
    "params": [
      439749085,
      3
    ]
  }'

const body = {
  "jsonrpc": "2.0",
  "id": 1,
  "method": "getSlotLeaders",
  "params": [
    439749085,
    3
  ]
};

const response = await fetch(process.env.THORNODE_RPC_URL, {
  method: "POST",
  headers: { "content-type": "application/json" },
  body: JSON.stringify(body),
});
const { result, error } = await response.json();
console.log(result ?? error);

{
  "jsonrpc": "2.0",
  "result": [
    "84gC25fbFKYueR9WEfreUysk1n3ZFxLFDDjbyqeqGpoW",
    "84gC25fbFKYueR9WEfreUysk1n3ZFxLFDDjbyqeqGpoW",
    "84gC25fbFKYueR9WEfreUysk1n3ZFxLFDDjbyqeqGpoW"
  ],
  "id": 1
}