Minted Token Asset ID

The asset ID of a token on the Fuel network is determined by two factors:

• The ID of the contract that minted the token,
• A sub-identifier (Sub ID)

Both of which are bits256 strings.

The process involves applying a SHA-256 hash algorithm to the combination of the Contract ID and the Sub ID, to derive an Asset ID - as explained here.

Consider the following simplified token contract:

contract;

use std::asset::{burn, mint, transfer};

abi Token {
    fn transfer_to_address(target: Address, asset_id: AssetId, coins: u64);
    fn transfer_to_contract(recipient: ContractId, asset_id: AssetId, coins: u64);
    fn mint_coins(sub_id: b256, mint_amount: u64);
    fn burn_coins(sub_id: b256, burn_amount: u64);
}

impl Token for Contract {
    fn transfer_to_address(recipient: Address, asset_id: AssetId, amount: u64) {
        transfer(Identity::Address(recipient), asset_id, amount);
    }

    fn transfer_to_contract(target: ContractId, asset_id: AssetId, amount: u64) {
        transfer(Identity::ContractId(target), asset_id, amount);
    }
    fn mint_coins(sub_id: b256, mint_amount: u64) {
        mint(sub_id, mint_amount);
    }

    fn burn_coins(sub_id: b256, burn_amount: u64) {
        burn(sub_id, burn_amount);
    }
}

See code in context

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Imagine that this contract is already deployed and we are about to mint some coins:

import { bn, getMintedAssetId } from 'fuels';

// Any valid bits256 string can be used as a sub ID
const subID = '0xc7fd1d987ada439fc085cfa3c49416cf2b504ac50151e3c2335d60595cb90745';
const mintAmount = bn(1000);

const { waitForResult } = await contract.functions.mint_coins(subID, mintAmount).call();
const txResult = await waitForResult();

const mintedAssetId = getMintedAssetId(subID, contract.id.toB256());

See code in context

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Since the asset ID depends on the contract ID, which is always dynamic (unlike the sub ID, which can be set to a fixed value), the helper getMintedAssetId can be used to easily obtain the asset ID for a given contract ID and sub ID.