# Build Calldata

The NiftyConnect exchange contract provides a method to build calldata which is necessary in `makeOrder` and `takeOrder`.

```js
const sellCalldata = await niftyConnectExchangeInst.buildCallData(
    ERC721TransferSelector, // uint selector,
    nftOwner, // address from,
    "0x0000000000000000000000000000000000000000", // address to,
    TestERC721.address,// address nftAddress,
    tokenId, // uint256 tokenId,
    ERC721_AMOUNT,// uint256 amount,
    "0x0000000000000000000000000000000000000000000000000000000000000000", // bytes32 merkleRoot
    [],// bytes32[] memory merkleProof
);

const buyCalldata = await niftyConnectExchangeInst.buildCallData(
    ERC721TransferSelector, // uint selector,
    "0x0000000000000000000000000000000000000000", // address from,
    buyer, // address to,
    TestERC721.address,// address nftAddress,
    tokenId, // uint256 tokenId,
    ERC721_AMOUNT,// uint256 amount,
    "0x0000000000000000000000000000000000000000000000000000000000000000", // bytes32 merkleRoot
    [],// bytes32[] memory merkleProof
);
```

The above is js example to call the util method.

| name        | type       | description                                                                                                               |
| ----------- | ---------- | ------------------------------------------------------------------------------------------------------------------------- |
| selector    | uint256    | Refer to [NFT Transfer Selector](https://docs.niftyconnect.org/niftyconnect-protocol-document/docs/nft-transfer-selector) |
| from        | address    | <p>NFTOwner address.<br>When making buy orders, leave it to zero.</p>                                                     |
| to          | address    | <p>NFT recipient address.<br>When making sell orders, leave it to zero.</p>                                               |
| nftAddress  | address    | NFT contract address                                                                                                      |
| tokenId     | uint256    | NFT asset token id                                                                                                        |
| amount      | uint256    | <p>For ERC721, the amount must be 1.<br>For ERC1155, its value should be no more than the nftOwner balance</p>            |
| merkleRoot  | bytes32    | Only used in trait-based order, leave it to zero for other scenarios                                                      |
| merkleProof | bytes32\[] | Only used in trait-based order, leave it to empty for other scenarios                                                     |