General info


In Unique Network, there is no need to write smart contracts as it is usually required in Ethereum networks.

Unique Network provides emulated smart contracts. This means that if you call a specific address where a smart contract is supposed to be, Unique Network will pretend that it has a smart contact there.
Thus, you can access our node using Ethereum technologies, and the node will respond.

This advantage allows using smart contracts just as libraries from any .js, .ts or even .sol file. This article will demonstrate how we call the smart contracts from
the @unique-nft/solidity-interfacesopen in new window library.


You need to have the following installed and prepared to start working with Unique Network
via Ethereum:

  • Node.js, version > 14.
  • npm or yarn.
  • Metamask account.

At the moment, we have Opal Testnet. Its websocket URL is wss://
(rpc endpoint -

In Polkadot apps, you can check it using this linkopen in new window.

You can use @unique2faucet_opal_botopen in new window in Telegram to get some OPL.

Set up environment

Install and initialize the libraries

First of all, we need to install the libraries. To install the required libraries, you can use the following commands. Please note that Hardhat must be initialized after the installation.

The second command will prompt to select the project type, please choose TypeScript and
answer yes to all questions.

npm install --save-dev hardhat @unique-nft/solidity-interfaces @unique-nft/utils @nomicfoundation/hardhat-toolbox dotenv
npx hardhat
npx hardhat test
yarn add -D hardhat @unique-nft/solidity-interfaces @unique-nft/utils @nomicfoundation/hardhat-toolbox @nomicfoundation/hardhat-network-helpers @nomicfoundation/hardhat-chai-matchers @nomiclabs/hardhat-ethers @nomiclabs/hardhat-etherscan chai ethers hardhat-gas-reporter solidity-coverage @typechain/hardhat typechain @typechain/ethers-v5 @ethersproject/abi @ethersproject/providers dotenv
yarn hardhat
yarn hardhat test 

Connect to network and Metamask account

Create a .env file in the root directory of our project, and add your Metamask private key and the network RPC to it. Follow these instructionsopen in new window to export your private key from Metamask.

Your .env should look like this:

PRIVATE_KEY = "your-metamask-private-key"

After this, update your hardhat.config.ts so that our project knows about all of these values.
Please pay attention to the settings object in the config file. To successfully compile the smart contracts, please use this configuration that enables the IR-based ( intermediate representation) code generator. Also, we will need to enable the optimizer and set the parameter for it.

This configuration is required for Solidity versions newer than 0.8.17 (for more details
please check the Solidity docsopen in new window).

import dotenv from 'dotenv'
import { HardhatUserConfig } from "hardhat/config";
import "@nomicfoundation/hardhat-toolbox";

const { RPC_OPAL, PRIVATE_KEY } = process.env;

const config: HardhatUserConfig = {
  solidity: {
    version: "0.8.17",
    settings: {
      metadata: {
        // Not including the metadata hash
        bytecodeHash: "none",
      optimizer: {
        enabled: true,
        runs: 800,
      viaIR : true,
  networks: {
    hardhat: {},
    opal: {
      url: RPC_OPAL,
      accounts: [`${PRIVATE_KEY}`]

export default config;

Write new smart contract

After this, we will write a new smart contract that will use this library. Please pay attention that we can just import a couple of .sol files and use them.

We will create a new file in the /contracts folder with the CollectionManager.sol name. This contract will create a collection and make it ERC721Metadata compatible. This simple example demonstrates how you can create your own smart contracts if needed using our library.

The contract below is inheritedopen in new window from CollectionHelpersEvents. You can refer to the CollectionHelpers.sol file from the library to learn more.
The contract contains one function (createCollection) that accepts a collection owner address, a collection admin address, a collection name, a collection description, a collection symbol and a collection base URI as arguments.
Then, the function calls the createNFTCollection function from our library that creates an NFT collection. When the collection is created, our function makes this collection ERC721Metadata compatible.
Finally, it sets the collection admin and collection owner and returns the address of the created collection.

// SPDX-License-Identifier: UNLICENSED
pragma solidity ^0.8.17;

import {CollectionHelpers, CollectionHelpersEvents} from  "@unique-nft/solidity-interfaces/contracts/CollectionHelpers.sol";
import {UniqueNFT, CrossAddress} from "@unique-nft/solidity-interfaces/contracts/UniqueNFT.sol";

// inherit contract from our interface 
contract CollectionManager is CollectionHelpersEvents {
  // a «static» smart contract in our chain (CollectionHelpers.sol) obtained by its address 
  CollectionHelpers helpers = CollectionHelpers(0x6C4E9fE1AE37a41E93CEE429e8E1881aBdcbb54F);

  function createCollection(
    address owner,
    address managerContract,
    string calldata name,
    string calldata description,
    string calldata symbol,
    string calldata baseURI
  ) public payable virtual returns (address){
    // create a collection using the method from the library 
    address collectionAddress = helpers.createNFTCollection{value: helpers.collectionCreationFee()}(name, description, symbol);
    // make the collection ERC721Metadata compatible
    helpers.makeCollectionERC721MetadataCompatible(collectionAddress, baseURI);
    // get the collection object by its address 
    UniqueNFT collection = UniqueNFT(collectionAddress);
    // set the collection admin and owner using cross address
    collection.addCollectionAdminCross(CrossAddress(managerContract, 0));
    collection.changeCollectionOwnerCross(CrossAddress(owner, 0));
    // return the collection address 
    return collectionAddress;

⚠️ Make sure that the version defined above (^0.8.17) is the same as the version defined
in the hardhat.config.ts file.

Deploy smart contract

Now, when our contract is written (see above) and our configuration file is ready, it is time to write the contract deployment script.

Create the deploy.ts file in the /scripts folder with the following content:

const {ethers} = require('hardhat');

async function main() {
  // Grab the contract factory
  const CollectionManager = await ethers.getContractFactory("CollectionManager");

  // Start deployment, returning a promise that resolves to a contract object
  const collectionManager = await CollectionManager.deploy(); // Instance of the contract
  console.log("Contract deployed to address:", collectionManager.address);


After this, we are finally ready to deploy our smart contract!
For this, please run the following command line:

npx hardhat run scripts/deploy.ts --network opal
yarn hardhat run scripts/deploy.ts --network opal

When the script is executed, you should then see something like:

Contract deployed to address: 0xB07956E26FDF1b215aC89AE21F822F8AB9Be9A27

Cross address

In this section, we would like to provide some details on how the cross address works in Ethereum. The cross address is a structure that contains an Ethereum and a Substrate addresses:

struct CrossAddress {
	address eth;
	uint256 sub;

⚠️ One of these addresses must be zero address. In other case, the blockchain will reject the transaction.

To clarify, you must specify two addresses in any case. But, one of them must be zero address, and the second one must be a valid address.

URI and URISuffix

A token has the following properties: baseURI, URI, URISuffix. In this section, we will provide some details about them and describe how an URI is returned by our tokenURI method when you are trying to get a token URI.

So, when we are getting a token URI, first of all, we need to check that this collection is ERC721Metadata compatible. If this is not so, the error will occur. Then, we check whether the mentioned above properties exist and are not zero address.

The check is carried out in this order: URI, baseURI, URISuffix.

  1. If the URI property is valid (exists and not zero address), then the method returns it.
    In case the property is invalid, proceed to next check.
  2. If the baseURI property is valid, then the method returns an empty value.
    In case the property is invalid, proceed to next check.
  3. If the URISuffix property is valid, the method returns the baseURI + URISuffix value.
  4. After all previous checks failed, the method returns the baseURI property value.

Thus, if the collection is not ERC721Metadata compatible, then you will not be able to get
the URI and URISuffix properties at all.