The ‘balance’ method must contain a function for retrieving the balance of a specific wallet from the state of the NFT object.

This is a crucial feature, as the control of all internal methods will depend on whether the function caller owns any instances of the token.

The balances of all owners are tracked in state.balances in the format of address: balance where balance is an integer.

The section below shows an example of a possible balance function:

export default function balance(state, action) {
  const input = action.input;
  const caller = action.caller;
  let target;
  if ( {
    target =;
  } else {
    target = caller;
  const ticker = state.ticker;
  const balances = state.balances;
    typeof target === "string",
    `Must specify target to retrieve balance for.`
  return {
    result: {
      balance: target in balances ? balances[target] : 0

This is only an example of the implementation, but can provides the default functionality needed for interoperability with existing Atomic NFT standards.

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