uint256 | Fixed size 256-bit math library | Math library

You need to instantiate the web3js.eth.Contract class with the new keyword.

this is a pointer to the current class instance, as in many other programming languages. You can for example point to public methods:

BscScan and EtherScan use the Transfer() event to update their statistics of token holders and to display amount of tokens transfered in the transaction detail page.

If you don't emit the event, it

• wouldn't display the "Tokens Transferred" field in the transaction detail page
• wouldn't update the token balance of the sender and receiver on Etherscan (e.g. on their address detail page)

But the contract would still transfer the tokens, and Etherscan would still show the transaction detail page (just without the tokens data).

Constructor public () - Warning: Visibility for constructor is ignored. If you want the contract to be non-deployable, making it "abstract" is sufficient.

The warning message says it all. You can safely remove the public visibility modifier because it's ignored anyway.

If you marked the BEP20Token contract abstract, you would need to have a child contract inheriting from it, could not deploy the BEP20Token itself, but would have to deploy the child contract. Which is not what you want in this case.

the second argument u passed is type 'float' instead of the required 'int'.

Your mintNFT() function doesn't emit any event containing the newItemId.

solidity is using the standard definition of transfer

There's no "standard definition", the ERC-721 standard only defines an interface and few other rules - and the actual implementation (of the interface) is on each developer. However I'm assuming that by the "standard definition" you mean the OpenZeppelin implementation, which is a widely used implementation of the ERC-721 standard and is used by many people who start coding in Solidity.

You can see in the linked implementation, that the OZ _mint() function emits the Transfer() event, where the 3rd argument is the minted token ID.

So executing your mintNFT() function effectively emits the Transfer() event that contains the newly minted token ID as a value of the 3rd parameter.

After you've executed the mintNFT() contract function from your JS code, it returns a PromiEvent object, that you can use to catch its receipt event.

The receipt contains the emited logs, where you can find the Transfer() log as well.

You can do that by waiting the promise, then assign the value:

The Using X for Y expression extends the Y datatype with functions of the X library.

In case of using SafeMath for uint256, it allows to use the functions defined in SafeMath (such as add()) on uint256 variables.

Specifically, function add() in SafeMath checks whether the addition would overflow the 256bit unsigned integer. If it did overflow, it throws an exception. If it didn't overflow, it returns the result of the addition.