Mastering Blockchain Programming with Solidity

The _isApprovedOrOwner internal function

_isApprovedOrOwner() is an internal function, which is used to check whether the given address of spender is approved or an owner of the given tokenId.

This function takes two arguments:

• spender: The address of the spender who is going to spend the given tokenId
• tokenId: The tokenId of the NFT that the spender wants to transfer

This function returns the Boolean result. If the result is as follows:

• true: The given spender is the owner or an approved address
• false: The given spender is neither the owner, nor the approved address

Let's look at the _isApprovedOrOwner() function code:

function _isApprovedOrOwner(address spender, uint256 tokenId) internal view returns (bool) {    address owner = ownerOf(tokenId) ...