Contract Integration

Tutorial 4 of 4

Introduction

Goal of the Tutorial

This tutorial aims to guide you on how to integrate a smart contract with your website or application. By the end of this tutorial, you will have learned how to create a secure, trustless system for transactions and interactions with your token.

Learning Outcomes

You will learn:
- The basics of smart contracts
- How to connect a smart contract with a website or application
- Best practices in contract integration

Prerequisites

You should have a basic understanding of:
- Web development (HTML, CSS, JavaScript)
- Solidity, the primary language for writing smart contracts
- Ethereum blockchain, as our smart contract will be hosted on this platform

Step-by-Step Guide

Creating a Smart Contract
- A smart contract is a self-executing contract with the terms of the agreement directly written into code. We will use Solidity to write our smart contract. Here's a Solidity tutorial to get you started.
Deploying the Contract on Ethereum Network
- Once the contract is written, it needs to be deployed on the Ethereum network. You can use tools like Truffle, a development environment, testing framework, and asset pipeline for Ethereum, to deploy your contract.
Connecting the Contract to your Website/Application
- We will use Web3.js, a collection of libraries that allow you to interact with a local or remote Ethereum node using HTTP, IPC, or WebSocket.

Code Examples

Here's an example of a simple Solidity contract:

// Version of Solidity compiler this program was written for
pragma solidity ^0.4.24;

// Our first contract is a simple one
contract SimpleContract {
    // Variable to store string
    string public myString;

    // Function to change the string
    function setMyString(string _myString) public {
        myString = _myString;
    }
}

In the contract above, we have declared a string variable myString and a function setMyString to modify that string. This is a very basic contract but should give you an idea of how contracts are written.

To interact with this contract through a website, we use Web3.js:

// First, we need to initialize web3
var web3;
if (typeof web3 !== 'undefined') {
    web3 = new Web3(web3.currentProvider);
} else {
    // set the provider you want from Web3.providers
    web3 = new Web3(new Web3.providers.HttpProvider("http://localhost:8545"));
}

// Then, we need to get the contract ABI (Application Binary Interface)
var ABI = [...]; // replace with your contract's ABI

// Then, we get the contract address
var Address = '...'; // replace with your contract's address

// Then, we initialize the contract
var contract = web3.eth.contract(ABI).at(Address);

// Finally, we can call our contract functions
contract.setMyString("Hello, world!");

In this script, we first initialize web3, then specify the ABI and address of our contract, and finally call our contract's function.

Summary

In this tutorial, you have learned:

What a smart contract is
How to write a smart contract using Solidity
How to deploy your contract on the Ethereum network
How to connect your contract to a website or application using Web3.js

Practice Exercises

Create a simple contract that stores and retrieves a number.
Deploy your contract on the Ethereum network.
Connect your contract to a simple HTML page where you can input and output the number.

Next Steps

Continue to explore and experiment with smart contracts and their integration. You may find the following resources useful: