Create A Simple Dapp

Tip

We will be building this app (opens new window)

Project Setup

Before you set up make sure you've visited and gone through our Getting Started Guide

Make sure you have:

1. The MetaMask Extension (opens new window) downloaded.
2. Node.js Downloaded and Installed (opens new window)
3. Clone/Download the Project Files (opens new window) from GitHub.
4. Your favorite Text Editor or IDE installed. I personally like Visual Studio Code (opens new window)

Open Project Folder

Open the project folder. Navigate to start->index.html, and look at the comment stating part 1. This is the UI for the Simple Dapp with all of the layout and buttons that will help us learn the basics of connecting to our MetaMask extension. We will be using/building off of this entire section for the first part of the tutorial.

Install Dependencies

Open a terminal and make sure your terminal is inside the base directory of the start/ folder. Inside the folder, the files should look like this:

.
├─ index.html
├─ contract.js
├─ metamask.css
├─ package.json
└─ README.md

You'll have some more files but that's nothing to worry about!

Open your terminal and navigate into the start folder. In this folder run:

yarn install

This will install all the necessary dependencies we'll need for our project. This will have created a node_modules/ folder where all the dependencies are stored.

Next run:

yarn run serve

Navigate to http://localhost:9011 (opens new window)

Basic Action(Part 1)

Now let's navigate into the contract.js file inside your start folder.

Your file should look something like this. Don't worry about lines 1-31.

const forwarderOrigin = 'http://localhost:9010';
const initialize = () => {
  //You will start here
};
window.addEventListener('DOMContentLoaded', initialize);

As soon as the content in the DOM is loaded we are calling our initialize function. Now before we start writing any code let's look at our task list for the first part of this app.

What we'll cover in part one:

• Connecting to the MetaMask Wallet
• See our eth_accounts result
• Display our network number
• Display our ChainId
• Display our Accounts

Connecting to the MetaMask Wallet

The first thing we need to do in our Dapp is to connect to our MetaMask Wallet.

1. We need to create a function to see if the MetaMask Chrome extension is installed
2. If MetaMask is not installed we:
   1. Change our connectButton to Click here to install MetaMask
   2. When clicking that button it should take us to a page that will allow us to install the extension
   3. Disable the button
3. If MetaMask is installed we:
   1. Change our connectButton to Connect
   2. When clicking that button it should allow us to connect to our MetaMask wallet
   3. Disable the button

Let's get to it!!

MetaMask Extension Check

In our code we need to connect to our button from our index.html

const initialize = () => {
  //Basic Actions Section
  const onboardButton = document.getElementById('connectButton');
};

Next we create a check function called isMetaMaskInstalled to see if the MetaMask extension is installed

const initialize = () => {
  //Basic Actions Section
  const onboardButton = document.getElementById('connectButton');
  //Created check function to see if the MetaMask extension is installed
  const isMetaMaskInstalled = () => {
    //Have to check the ethereum binding on the window object to see if it's installed
    const { ethereum } = window;
    return Boolean(ethereum && ethereum.isMetaMask);
  };
};

Next we need to create a MetaMaskClientCheck function to see if we need to change the button text based on if the MetaMask Extension is installed or not.

const initialize = () => {
  //Basic Actions Section
  const onboardButton = document.getElementById('connectButton');
  //Created check function to see if the MetaMask extension is installed
  const isMetaMaskInstalled = () => {
    //Have to check the ethereum binding on the window object to see if it's installed
    const { ethereum } = window;
    return Boolean(ethereum && ethereum.isMetaMask);
  };
  //------Inserted Code------\\
  const MetaMaskClientCheck = () => {
    //Now we check to see if MetaMask is installed
    if (!isMetaMaskInstalled()) {
      //If it isn't installed we ask the user to click to install it
      onboardButton.innerText = 'Click here to install MetaMask!';
    } else {
      //If it is installed we change our button text
      onboardButton.innerText = 'Connect';
    }
  };
  MetaMaskClientCheck();
  //------/Inserted Code------\\
};

MetaMask "Not Installed" Dapp Flow

In our code block where MetaMask isn't installed and we ask the user to 'Click here to install MetaMask!', we need to ensure that if our button is clicked we:

1. Redirect the user to the proper page to install the extension
2. Disable the button

const MetaMaskClientCheck = () => {
  //Now we check to see if Metmask is installed
  if (!isMetaMaskInstalled()) {
    //If it isn't installed we ask the user to click to install it
    onboardButton.innerText = 'Click here to install MetaMask!';
    //When the button is clicked we call this function
    onboardButton.onclick = onClickInstall;
    //The button is now disabled
    onboardButton.disabled = true;
  } else {
    //If it is installed we change our button text
    onboardButton.innerText = 'Connect';
  }
};
MetaMaskClientCheck();

We've created a function that will be called when we click the button and disable it. Let's dive into the onClickInstall function and create the logic inside of it.

Tip

For this part we will be using the '@metamask/onboarding' library we installed during the npm install. To learn more visit here (opens new window)

Inside this function we want to:

1. Change the text of the button to Onboarding in progress
2. Disable the button
3. Start the onboarding process

Above your MetaMaskClientCheck function write/insert this code.

//We create a new MetaMask onboarding object to use in our app
const onboarding = new MetaMaskOnboarding({ forwarderOrigin });
//This will start the onboarding proccess
const onClickInstall = () => {
  onboardButton.innerText = 'Onboarding in progress';
  onboardButton.disabled = true;
  //On this object we have startOnboarding which will start the onboarding process for our end user
  onboarding.startOnboarding();
};

GREAT! Now if our end user doesn't have the MetaMask Extension they can install it. When they refresh the page the ethereum window object will be there and we can get on to connecting their MetaMask wallet to our Dapp!

MetaMask "Installed" Dapp Flow

Next we need to revisit our MetaMaskClientCheck function and create similar functionality that we did in our "MetaMask Not Installed" block in our "MetaMask Is Installed" block of code.

const MetaMaskClientCheck = () => {
  //Now we check to see if Metmask is installed
  if (!isMetaMaskInstalled()) {
    //If it isn't installed we ask the user to click to install it
    onboardButton.innerText = 'Click here to install MetaMask!';
    //When the button is clicked we call th is function
    onboardButton.onclick = onClickInstall;
    //The button is now disabled
    onboardButton.disabled = true;
  } else {
    //If MetaMask is installed we ask the user to connect to their wallet
    onboardButton.innerText = 'Connect';
    //When the button is clicked we call this function to connect the users MetaMask Wallet
    onboardButton.onclick = onClickConnect;
    //The button is now enabled
    onboardButton.disabled = false;
  }
};
MetaMaskClientCheck();

Now we've created a function that will be called whenever we click the button to trigger a connection to our wallet, disabling the button. Next, let's dive into the onClickConnect function and build the logic we need inside of it.

Inside this function we want to:

1. Create an async function that will try to call the 'eth_requestAccounts' RPC method
2. Catch any errors and log them to the console

Under your onClickInstall function write/insert this code.

const onClickConnect = async () => {
  try {
    // Will open the MetaMask UI
    // You should disable this button while the request is pending!
    await ethereum.request({ method: 'eth_requestAccounts' });
  } catch (error) {
    console.error(error);
  }
};

Great! Now once you click the button the MetaMask Extension will pop up and connect your wallet.

Get Ethereum Accounts

After this what we'd like to do next is whenever we press the eth_accounts button we'd like to get our Ethereum account and display it. Replace the existing const onboardButton at the top of the initialize() function with the following three buttons:

//Basic Actions Section
const onboardButton = document.getElementById('connectButton');
const getAccountsButton = document.getElementById('getAccounts');
const getAccountsResult = document.getElementById('getAccountsResult');

Now that we've grabbed our eth_accounts button and our paragraph field to display it in we now have to grab the data.

Under our MetaMaskClientCheck() function let's write/insert the code below.

//Eth_Accounts-getAccountsButton
getAccountsButton.addEventListener('click', async () => {
  //we use eth_accounts because it returns a list of addresses owned by us.
  const accounts = await ethereum.request({ method: 'eth_accounts' });
  //We take the first address in the array of addresses and display it
  getAccountsResult.innerHTML = accounts[0] || 'Not able to get accounts';
});

If you have already connected to your wallet in the previous section of the tutorial, you can go into MetaMask's "Connected Sites" menu and remove the localhost connection. This will enable us to test both buttons again. If we refresh our page, and click the "ETH_ACCOUNTS" button, we should see 'eth_accounts result: Not able to get accounts'.

Let's go ahead and press the "Connect" button again, and confirm the "Connect With MetaMask" prompt and "Connect". Now we can click the "ETH_ACCOUNTS" button again and we should see our MetaMask account public address.

CONGRATULATIONS!

We have just completed building out our Basic Actions functionality. You know how to Connect to MetaMask, see your connected apps and remove them, as well as retrieve accounts.

Now on to our next step, showing our statuses.

Preview of the completed code up until this point of the tutorial:

const forwarderOrigin = 'http://localhost:9010';
const initialize = () => {
  //Basic Actions Section
  const onboardButton = document.getElementById('connectButton');
  const getAccountsButton = document.getElementById('getAccounts');
  const getAccountsResult = document.getElementById('getAccountsResult');
  //Created check function to see if the MetaMask extension is installed
  const isMetaMaskInstalled = () => {
    //Have to check the ethereum binding on the window object to see if it's installed
    const { ethereum } = window;
    return Boolean(ethereum && ethereum.isMetaMask);
  };
  //We create a new MetaMask onboarding object to use in our app
  const onboarding = new MetaMaskOnboarding({ forwarderOrigin });
  //This will start the onboarding proccess
  const onClickInstall = () => {
    onboardButton.innerText = 'Onboarding in progress';
    onboardButton.disabled = true;
    //On this object we have startOnboarding which will start the onboarding process for our end user
    onboarding.startOnboarding();
  };
  const onClickConnect = async () => {
    try {
      // Will open the MetaMask UI
      // You should disable this button while the request is pending!
      await ethereum.request({ method: 'eth_requestAccounts' });
    } catch (error) {
      console.error(error);
    }
  };
  const MetaMaskClientCheck = () => {
    //Now we check to see if Metmask is installed
    if (!isMetaMaskInstalled()) {
      //If it isn't installed we ask the user to click to install it
      onboardButton.innerText = 'Click here to install MetaMask!';
      //When the button is clicked we call th is function
      onboardButton.onclick = onClickInstall;
      //The button is now disabled
      onboardButton.disabled = false;
    } else {
      //If MetaMask is installed we ask the user to connect to their wallet
      onboardButton.innerText = 'Connect';
      //When the button is clicked we call this function to connect the users MetaMask Wallet
      onboardButton.onclick = onClickConnect;
      //The button is now disabled
      onboardButton.disabled = false;
    }
  };
  //Eth_Accounts-getAccountsButton
  getAccountsButton.addEventListener('click', async () => {
    //we use eth_accounts because it returns a list of addresses owned by us.
    const accounts = await ethereum.request({ method: 'eth_accounts' });
    //We take the first address in the array of addresses and display it
    getAccountsResult.innerHTML = accounts[0] || 'Not able to get accounts';
  });
  MetaMaskClientCheck();
};
window.addEventListener('DOMContentLoaded', initialize);