Ethereum Cookbook

How to do it...

For writing data to smart contracts, we have to follow this procedure:

1. Consider the following example contract:

pragma solidity ^0.4.21;contract HelloWorld {    // State variable    string textToPrint = "hello world";    // State changing function    function changeText(string _text) public {        textToPrint = _text;    }    // Read-only function    function printSomething() public view returns (string) {        return textToPrint;    }}

2. Create the contract instance with the ABI and the deployed address. The method to create an instance is slightly different between web3.js v0.2x.x and v1.x.x:

// For v0.2x.xvar helloWorld = web3.eth.contract(<ABI>);
var helloWorldInstance = helloWorld.at("<Address>");// For v1.x.xvar helloWorldInstance = new web3.eth.