Solidity Hello World

index.html

<pre>
pragma solidity >=0.4.22 <0.6.0;

contract hello {

    function getHelloWorld () public returns (string memory) {
        return 'hello world';
    }

} 
</pre>
<script src="https://raw.githubusercontent.com/leon-do/Offchain-Ethereum-Wallet/master/js/lib/web3.minjs"></script>
<div id="displayText"></div>

<button onclick="callContractFunction()">
  click to call the "getHelloWorld" function on the blockchain
</button>

<!-- This exposes the library as a global variable: web3 -->
<script src="./web3.min.js"></script>

<script>
  /**
    use truffle or remix.ethereum.org to deploy hello.sol
    to interact you need 3 things
    0. network: the network I chose is rinkeby testnet
    1. contract address: once deployed you should get a contract address
    2. abi: is used to interact interface with machine code: example here https://solidity-compiler.herokuapp.com/
   */
  // connect to testnet
  web3 = new Web3(
    new Web3.providers.HttpProvider('https://rinkeby.infura.io/')
  );
  //     https://rinkeby.etherscan.io/address/0xda6ccc32328d09bf54a16b8c27b1158af56522d8
  const contractAddress = '0xda6ccc32328d09bf54a16b8c27b1158af56522d8';
  // used to interact with machine code
  const abi = [
    {
      constant: false,
      inputs: [],
      name: 'getHelloWorld',
      outputs: [
        {
          internalType: 'string',
          name: '',
          type: 'string'
        }
      ],
      payable: false,
      stateMutability: 'nonpayable',
      type: 'function'
    }
  ];
  async function callContractFunction() {
    // https://web3js.readthedocs.io/en/v1.2.0/web3-eth-contract.html?highlight=estimateGas#id18
    new web3.eth.Contract(abi, contractAddress).methods
      .getHelloWorld()
      .call()
      .then(data => {
        alert(data);
      });
  }
</script>