Hey everybody, this is the second post of the series on writing apps the Git way, where you just go take a cup of coffee and browse a Git repo to learn something new! Be sure to take it step by step, if you're a new kid on the block. Today we're going to write a Node.js app for the purpose to interact with our shiny new first Solidity smart contract deployed on the Ropsten testnet already -- which remember, basically outputs the string. Hello world! The code is available at . programarivm/solidity-interacting-with-nodejs Here is the git log for you to get the application up and running. $ git log --oneline
45e59bd (HEAD -> master) app.js is implemented
80195ad npm install web3 dotenv
97a0d34 .gitignore is added
fdd0e78 npm init As you can see in commit , our is really really simple. 45e59bd app.js ( ).config() ; Web3 = ( ); infuraKey = process.env.INFURA_KEY; web3 = Web3( Web3.providers.HttpProvider( )); helloWorld = web3.eth.Contract([
  { : , : [], : , : [
      { : , : , : }
    ], : , : , : }
], );

helloWorld.methods.output().call({ : }, { .log(result);
}); require 'dotenv' const require 'web3' const const new new `https://ropsten.infura.io/v3/ ` ${infuraKey} const new "constant" true "inputs" "name" "output" "outputs" "internalType" "string" "name" "" "type" "string" "payable" false "stateMutability" "pure" "type" "function" '0x35c113E1AB11B3001e9085CBafD224FfC3470C67' from '0x8863ae48646c493efF8cd54f9Ffb8Be89669E62A' ( ) function error, result console This is how to output the message: $ node app.js
Hello world! There are just two things to be noted. In the first place we're using , the Ethereum JavaScript API, for to interact with the smart contract. web3 app.js Web3 = ( ); const require 'web3' Secondly, the JSON representation of the contract's application binary interface (ABI) is passed as a parameter when creating a new contract object. helloWorld = web3.eth.Contract([
  { : , : [], : , : [
      { : , : , : }
    ], : , : , : }
], ); const new "constant" true "inputs" "name" "output" "outputs" "internalType" "string" "name" "" "type" "string" "payable" false "stateMutability" "pure" "type" "function" '0x35c113E1AB11B3001e9085CBafD224FfC3470C67' Given the fact that the smart contract's method is quite basic, meaning its state is not being altered, the simplest possible way to run the method for learning purposes is probably through web3's function. output() call() helloWorld.methods.output().call({ : }, { .log(result);
}); from '0x8863ae48646c493efF8cd54f9Ffb8Be89669E62A' ( ) function error, result console That's it! In future posts, I'll show you a little bit of error handling. You may also be interested in... The Git Way to Deploy a Solidity Contract on Ropsten With Truffle The web3.js library

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