Web3.js Development – Get Contract ABI Knowing Only Contract Address

I know the question is old, but I had some problems with this so I will share what helped me.

To import the ABI from a JSON file, you can use the following code (assuming you already have your web3 Object):

var fs = require('fs');
var jsonFile = "pathToYourJSONFile/project.json";
var parsed= JSON.parse(fs.readFileSync(jsonFile));
var abi = parsed.abi;

var YourContract= new web3.eth.Contract(abi, 0x12345678912345678912345678912345678912);

You can read more about it here: https://web3js.readthedocs.io/en/1.0/web3-eth-contract.html

Update 01/2020: Since Typescript 2.9, reading JSON Files is supported directly. So if you try to get the ABI or Bytecode from within a Typescript Project (Angular, React, ...) simply go to your tsconfig.json and set:

{
  "compilerOptions": {
    "resolveJsonModule": true,
    "esModuleInterop": true  
  }
}

You can then use import ContractName from 'path/to/contract/ContractName.json' to import your Contracts and get the Abi with ContractName.abi.

Cheers

The page "Verify Contract" ask for "Constructor Arguments ABI-encoded".

In your case the constructor has no parameters, so you can leave such field empty.

In the general case when your constrctor has parameters you can proceed as follow:

You can use ethereumjs-abi to encode/decode the parameters for transaction calls.

Let's suppose your constructor is MyToken(address _to, uint256 _value, bool _enabled). The parameters types are ["address", "uint256", "bool"].

If you have created the contract MyToken("0x1234567812345678", 0x314159268, true). Then the parameters values are ["0x1234567812345678", "0x314159268", true].

Then you can encode the values with rawEncode(parameterTypes, parameterValues).

var abi = require('ethereumjs-abi')

var parameterTypes = ["address", "uint256", "bool"];
var parameterValues = ["0x1234567812345678", "0x314159268", true];

var encoded = abi.rawEncode(parameterTypes, parameterValues);

console.log(encoded.toString('hex'));

On execution it will output

000000000000000000000000000000000000000000000000123456781234567800000000000000000000000000000000000000000000000000000003141592680000000000000000000000000000000000000000000000000000000000000001