Which RPC command does web3.js use to call into an arbitrary smart contract function?

Question

I am trying to duplicate some of the function of web3.js in C++. I don't really know much javaScript. I can see how the code calls into simple RPC calls such as eth_getBlockByNumber or eth_getTransactionByHash. That's easy enough.

I can't figure out how web3.js calls one of the functions on a smart contract though. For example, how does it call a function like an ERC20 token getTotalSupply?

I'm not looking for Javascript code explain how to use the capability, but instead the code that implements the functionality.

Answer 1

To call a function on contract web3 has to first instantiate the contract and that capability is implemented at https://github.com/ethereum/web3.js/blob/develop/lib/web3/contract.js#L262-L274

Then we can send requests to the contract and that capability is implemented at https://github.com/ethereum/web3.js/blob/develop/lib/web3/function.js