Greetings - Say Hello to Ethereum

Sample Ethereum smart contract using Metamask, Truffle 5, Ganache and web3.js 1.x.

Follow the steps described below to install, deploy and run the Dapp.

Warning

Make that you don't run your tests on the Ethereum's main net otherwise you will spend real ether with no chance to get it back

Prerequisites: Install tools and frameworks

To build, deploy and test your Dapp locally, you need to install the following tools and frameworks:

• node.js and npm: https://nodejs.org/en/

  • Node.js can be installed from an installation package or through some package managers such as Homebrew on a Mac.

• Truffle: https://github.com/trufflesuite/truffle

  • Create and deploy your Dapp with this build framework for Ethereum.

  In this sample, we use the beta version of Truffle 5 that you can install in this way:

  npm uninstall -g truffle
  npm install -g truffle
  

• Ganache: https://github.com/trufflesuite/ganache

  • Development Ethereum node.

Step 1. Clone the project

`git clone https://github.com/chainskills/greetings-truffle5.git

Step 2. Start your Ethereum node

Start Ganache.

The first account will be the default account used to deploy your contract.

Step 3. Configure your project

Edit your file truffle-config.js to set the port number used by Ganache.

Step 4. Test your project

Truffle uses Mocha and Chain to run your tests.

$ truffle test --network ganache

Step 5. Compile and deploy your smart contract

$ truffle migrate --reset --compile-all --network ganache

The output will provide you useful information such as the total cost of your deployment.

Step 6. Open the Truffle console

We will use the console from Truffle to interact with the smart contract:

$ truffle console --network ganache
truffle(ganache)>

Step 7: Fetch all accounts

Before interacting with the smart contract, we have to fetch the accounts defined in Ganache:

truffle(ganache)> accounts = await web3.eth.getAccounts()

You can list your accounts:

truffle(ganache)> accounts

Step 8: Get an instance to your deployed smart contract

We create an instance to our smart contract.

truffle(ganache)> greetings = new web3.eth.Contract(Greetings.abi, Greetings.address)

From now on, you can use the app variable to interact with your smart contract.

Step 9: Get the default greetings message

The constructor of the smart contract has set a default greetings message:

truffle(ganache)> await greetings.methods.getGreetings().call()
'I am ready!'

You should see "I'm ready!".

At this stage you can open the Transactions page on Ganache. You will notice that this call is free because the getGreetings() function is a constant.

Step 10: Change the greetings message

The call to this function will require some gas as we will change the state of the smart contract:

truffle(development)> await greetings.methods.setGreetings("Hello from ChainSkills!").send({from: accounts[1]})

If you review the Transactions page on Ganache you will find a "CONTRACT CALL" transaction. Please inspect it to review the gas paid by the accounts[1]. The data is coded in hexadecimal.

Step 11: Check the updated greetings message

The new greetings message should be displayed using the getGreetings() function call:

truffle(ganache)> await greetings.methods.getGreetings().call()
'Hello from ChainSkills!'

Learn more

If you want to know more about all the steps required to install, build and deploy a Dapp, you can subscribe to our course available on Udemy: https://www.udemy.com/getting-started-with-ethereum-solidity-development

We have also a lean-published ebook available on leanpub: https://leanpub.com/blockchain-developer

Have fun !!!

ChainSkills Team - 2019