Calling contract functions using only ABI without source code

Question

I have MyContract.json file of some contract(assume i haven't its source code). In .json file, there is abi and bytecode. If i want to deploy such contract (through web3js), I am facing following problems. However, this question becomes more complex, when there are thousand of contracts, which is my final task. But here i am just limit my self to only one contract for understanding purpose.

1. If such contract need some arguments in its constructor, then how can i know its parameters with valid values, so that it could be deployed, successfully.
2. How can I call its different functions (getters, setters)?

For question no. 1; I am sharing here my code for its deployment. It is valid and working if contract has constructor which take owner address in its parameter. This code is tested on some known contract with source code. However, if constructor takes no parameters or different parameters or lot of other parameters, this code will fail to deploy, because i must have to pass valid number of parameters and valid values.

var compiledContract = require('./build/MyContract.json');

async function deployCon() {

const contract = new web3.eth.Contract(compiledContract.abi);
const params = {
    data: '0x' + compiledContract.bytecode,
    arguments: [account1]
};
const transaction = contract.deploy(params); 
const options = {
    data: transaction.encodeABI(),
    gas: await transaction.estimateGas({from: account1})
};
// console.log(options)
const signed = await web3.eth.accounts.signTransaction(options, privateKey1);
receipt = await web3.eth.sendSignedTransaction(signed.rawTransaction);
console.log(`Contract deployed at address: ${receipt.contractAddress}`);
return receipt;

}

For question no. 2; i am totally blind how to call contract's functions shown here as ??????? (which will come to know through abi of .json file alongwith parameters!).

var  myContAddr = receipt.contractAddress;
    var myContractAbiDefenition = compiledContract.abi;
    var myContractInstance = new web3.eth.Contract(myContractAbiDefenition, myContAddr);
    await myContractInstance.methods.???????.send({from: account1, value: web3.utils.toWei(amount, 'ether')})

Answer 1

For your question no. 1: Search for "type": "constructor" in your ABI. From this object, you can see the inputs that has an array of parameters along with their name and type. Example:

  {
    "inputs": [
      {
        "internalType": "uint256",
        "name": "_ff",
        "type": "uint256"
      },
      {
        "internalType": "string",
        "name": "_name",
        "type": "string"
      }
    ],
    "payable": false,
    "stateMutability": "nonpayable",
    "type": "constructor"
  }

In the above example, you can see the constructor has two parameters: _ff and name of type uint256 and string respectively.

For question no. 2: once the contract is instantiated, you can log all the methods as well as public state variable, by using console.log(myContractInstance.methods).

Otherwise, you can look into ABI where type is function. But this is may be a more complex way.

Updated:

let abi = JSON ABI;

for (let item of abi) {
    // this will return an array of constructor parameters along with their name and type
    if (item.type === "constructor") console.log(item.inputs);
    // result [{internalType: "uint256", name: "_ff", type: "uint256"}, {internalType: "string", name: "_name", type: "string"}]

    // this will return only the names
    // you can push the names into array
    // then iterate over the array to call them
    if (item.type === "function") console.log(item.name);
}

Hope it will help.