why do i see input data in the transaction details when i didn't pass it as a data parameter

Question

When I create a transaction like below

 App.contracts.Soccer.deployed().then(function(instance) {       
    return instance.purchaseShoes(name, age, { from: accounts[0], value: value});
 }).then(function() {
 ...

it creates an input data in transaction details from etherscan. Isn't input data only created when I passed it as a data parameter? (ex: { from: accounts[0], value: value, data: 'test data' }

When I decoded the input data by converting it to utf-8 from etherscan, although it was not totally readable, I saw one of the values were the data I passed it to purchseShoes function.

So my question is, why is it creating an input data when I didn't pass it as a data param? how can I prevent it from creating it?

Answer 1

The data you saw are exactly the data you passed as name, age. The web3, in the background packs function name, input parameters and so on in the data field of transaction so the EVM knows what function it should execute and what are the parameters for it. You can see in this asnwer how the data are created and encoded and then added to the transaction before the transaction is finally singed, you can see creation and signing of tx at the bottom.

I'm not really sure what web3 does to that data object in the last parameter, probably ignores it (my best guess). Params from that object are related to the transaction itself, like what account to use for signing, how many wei to send, gas limit, gas price etc.