naijatechbro / a-guide-to-dapps

Are you new to web3 and you want to write your first smart contract the easiest way? Try this tutorial

A-Guide-to-Dapps

Are you new to web3 and you want to write your first smart contract the easiest way? Try this tutorial

Preparation

Download and Install MetaMask

Never used Metamask? Watch this explainer video

The important bits for us are: 1:06 to 4:14

Click Ethereum Mainnet in the top. Change to the Ropsten Tesnet and get a copy of the account's public address on your Metamask Wallet.

Request some Ropsten Tesnet Ether from a faucet loaded into your Metamask Wallet.

Faucet link to request funds

https://testnet.help/en/ethfaucet/ropsten Blog explaining a faucet and how to use one Install a http server. Use any you like, but we recommend lite-server for beginners:

Install Node.js (Download and Instructions) Install lite-server (with NPM in a terminal/command prompt): npm install -g lite-server #install lite-server globally Create and Serve a Simple Webpage The first step is to create a basic HTML page.

Create a new folder (directory) in your terminal using mkdir In a code editor (e.g. Atom, or Visual Studio Code), open the folder Create a new file called index.html Open index.html Create HTML boilerplate

<title>My First dApp</title> We will create an app that simply reads and writes a value to the blockchain. We will need a label, an input, and buttons.

Inside the body tag, add some text, a label and input.

This is my dApp!

Here we can set or get the mood:

Input Mood:

Inside the div tag add some buttons. Get Mood Set Mood OPTIONAL: Inside the tag, add some styles to make it look nicer <style> body { text-align: center; font-family: Arial, Helvetica, sans-serif; } div { width: 20%; margin: 0 auto; display: flex; flex-direction: column; } button { width: 100%; margin: 10px 0px 5px 0px; } </style>

Serve the webpage via terminal/command prompt from the directory that has index.html in it and run:

lite-server

Go to http://127.0.0.1:3000/ in your browser to see your page!

Your front end is now complete!

Create a Basic Smart Contract

Now it's time to create a Solidity smart contract.

You can use any editor you like to make the contract. For this tutorial we recommend the online IDE Remix

Never used Remix before? Checkout This video Go to Remix

Check out the "Solidity Compiler", and "Deploy and Run Transactions" tabs. If they are not present, enable them in the plugin manager

Create a new solidity file in remix, named mood.sol

Write the contract

Specify the solidity version and add a license // SPDX-License-Identifier: MIT pragma solidity ^0.8.1; Define the contract contract MoodDiary{

} Inside the contract create a variable called mood string mood; Next, create Read and Write functions //create a function that writes a mood to the smart contract function setMood(string memory _mood) public{ mood = _mood; }

//create a function the reads the mood from the smart contract function getMood() public view returns(string memory){ return mood; } And that's it! Your code should look like this Deploy the contract on the Ropsten Testnet.

Make sure your Metamask is connected to the Ropsten Testnet. Make sure you select the right compiler version to match the solidity contract. (In the compile tab) Compile the code using the "Solidity Compiler" tab. Note that it may take a moment to load the compiler Deploy the contract under the "Deploy and Run Transactions" tab Under the Deployed Contracts section, you can test out your functions on the Remix Run tab to make sure your contract works as expected! Be sure to deploy on Ropsten via Remix under the Injected Web3 environment and confirm the deployment transaction in Metamask

Make a new temporary file to hold:

The deployed contract's address Copy it via the copy button next to the deployed contracts pulldown in remix's Run tab The contract ABI (what is that?) Copy it via the copy button under to the contract in remix's Compile tab (also in Details) Connect Your Webpage to Your Smart Contract Back in your local text editor in index.html, add the following code to your html page:

Import the Ethers.js source into your index.html page inside a new set of script tags:

<script src="https://cdn.ethers.io/lib/ethers-5.2.umd.min.js" type="application/javascript" ></script> <script> //////////////////// //ADD YOUR CODE HERE //////////////////// </script>

Inside the script tag, import the contract ABI (what is that?) and specify the contract address on our provider's blockchain: const MoodContractAddress = ""; const MoodContractABI = let MoodContract; let signer; For the contract ABI, we want to specifically navigate to the JSON Section. We need to describe our smart contract in JSON format.

Since we have two methods, this should start as an array, with 2 objects:

const MoodContractABI = [{}, {}] From the above page, each object should have the following fields: constant, inputs, name, outputs, payable, stateMutability and type.

For setMood, we describe each field below:

name: setMood, self explanatory type: function, self explanatory outputs: should be [] because this does not return anything stateMutability: This is nonpayable because this function does not accept Ether inputs: this is an array of inputs to the function. Each object in the array should have internalType, name and type, and these are string, _mood and string respectively For getMood, we describe each field below:

name: getMood, self explanatory type: function, self explanatory outputs: this has the same type as inputs in setMood. For internalType, name and type, this should be string, "", and string respectively stateMutability: This is view because this is a view function inputs: this has no arguments so this should be [] Your end result should look like this:

const MoodContractABI = [ { "inputs": [], "name": "getMood", "outputs": [ { "internalType": "string", "name": "", "type": "string" } ], "stateMutability": "view", "type": "function" }, { "inputs": [ { "internalType": "string", "name": "_mood", "type": "string" } ], "name": "setMood", "outputs": [], "stateMutability": "nonpayable", "type": "function" } ]

Next, Define an ethers provider. In our case it is Ropsten:

const provider = new ethers.providers.Web3Provider(window.ethereum, "ropsten"); Request access to the user's wallet and connect the signer to your metamask account (we use [0] as the default), and define the contract object using your contract address, ABI, and signer provider.send("eth_requestAccounts", []).then(() => { provider.listAccounts().then((accounts) => { signer = provider.getSigner(accounts[0]); MoodContract = new ethers.Contract( MoodContractAddress, MoodContractABI, signer ); }); }); Create asynchronous functions to call your smart contract functions async function getMood() { const getMoodPromise = MoodContract.getMood(); const Mood = await getMoodPromise; console.log(Mood); }

async function setMood() { const mood = document.getElementById("mood").value; const setMoodPromise = MoodContract.setMood(mood); await setMoodPromise; } Connect your functions to your html buttons Get Mood Set Mood

Test Your Work Out!

Got your webserver up? Go to http://127.0.0.1:3000/ in your browser to see your page! Test your functions and approve the transactions as needed through Metamask. Note block times are ~15 seconds... so wait a bit to read the state of the blockchain See your contract and transaction info via https://ropsten.etherscan.io/ Open a console (Ctrl + Shift + i) in the browser to see the magic happen as you press those buttons DONE! Celebrate! You just made a webpage that interacted with a real live Ethereum testnet on the internet! That is not something many folks can say they have done!

If you had trouble with the tutorial, you can try out the example app provided.

git clone https://github.com/NaijaTechBro/A-Guide-to-Dapp cd BasicFrontEndTutorial lite-server Try and use the following information to interact with an existing contract we published on the Roptsen testnet: We have a MoodDiary contract instance created at this transaction

Here is the contract (on etherscan)

We also verified our source code to ropsten.etherscan.io as an added measure for you to verify what the contract is exactly, and also the ABI is available to the world! The ABI is also in this file

This illustrates an important point: you can also build a dApp without needing to write the Ethereum contract yourself! If you want to use an existing contract written and already on Ethereum, you can!