Writing your own extensions

You can create your own extensions. They are just regular functions that pre-define the behavior of a prepareContractCall() or readContract() function.

The goal of extensions is to add a layer of convenience to direct contract calls, either to simplify the inputs or to give richer outputs.

The erc20/getBalance extension is a very convenient and efficient way to fetch all the information needed to display an ERC20 token balance to a user, a very common usecase for applications. Here is how it is implemented in the SDK.

// Define your extension function
export function getBalance(
	// The base options include everything that is needed to interact with the contract, *except* the specific params for your function, in this case, "address"
	options: BaseTransactionOptions<{ address: string }>,
) {
	// The extension conveniently fetches all the relevant information from the contract to display a readable balance
	const [balanceWei, decimals_, symbol_, name_] = await Promise.all([
		balanceOf(options),
		decimals(options),
		symbol(options),
		name(options),
	]);
	return {
		value: balanceWei,
		decimals: decimals_,
		// The `toTokens` function converts the balance from wei to a human-readable format
		displayValue: toTokens(balanceWei, decimals_),
		symbol: symbol_,
		name: name_,
	};
}

The erc721/mintTo extension handles uploading the NFT metadata to IPFS before minting. Here is how it is implemented in the SDK.

import {
  prepareContractCall,
  type BaseTransactionOptions,
} from "thirdweb";
 
// Define your extension function
export function mintTo(
  // The base options include everything that is needed to interact with the contract, *except* the specific params for your function, in this case "to" and "nft"
  options: BaseTransactionOptions<{ to: string; nft: NFTMetadata }>,
) {
  return prepareContractCall({
    // Pass the contract from the options
    contract: options.contract,
    // Pre-define the function to call on the smart contract
    method: "function mintTo(address to, string uri)",
    // The function params can be async
    params: async () => {
      // Upload the metadata to IPFS
      const tokenURI = (await upload({
        client: options.contract.client,
        files: [options.nft],
      })[0]) as string;
      // return the contract params
      return [options.to, tokenURI] as const;
    },
  });
}