A Hello World style starter project. Deploys a smart contract with a message, and renders it in the front-end. You can change the message using the interact panel!
This dapp implements a "Hello World" style application that echoes a message passed to the contract to the front end. This tutorial is intended to be followed using the online IDE available at Remix IDE.
Remix IDE - an online IDE to develop smart contracts.
If you’re new to Remix, You’ll first need to activate two modules: Solidity Compiler and Deploy and Run Transactions.
search for 'Solidity Compiler' and 'Deploy and Run Transactions' plugins in the plugin tab in Remix
Activate the two plugins
Select Solidity Environment
- Go to File Explorers, And Create a new file , Name it HelloWorld.sol
Copy/Paste the Smart contract below into the newly created file
The smart contract
The first line,
pragma solidity ^0.5.10 specifies that the source code is for a Solidity version greater than 0.5.10. Pragmas are common instructions for compilers about how to treat the source code (e.g., pragma once).
A contract in the sense of Solidity is a collection of code (its functions) and data (its state) that resides at a specific address on the Ethereum blockchain. The line
string public message declares a public state variable called
message of type
string. You can think of it as a single slot in a database that you can query and alter by calling functions of the code that manages the database. The keyword public automatically generates a function that allows you to access the current value of the state variable from outside of the contract. Without this keyword, other contracts have no way to access the variable.
The constructor is a special function run during the creation of the contract and cannot be called afterward. In this case, it takes a string value
initMessage, stores the value in the memory data storage area, and sets
message to that value.
string public message function is another public function that is similar to the constructor, taking a string as a parameter, and updating the
Compile Smart Contract
- Go to Solidity Compiler
- Select Compiler Version to 0.5.10
- After Successful Compilation, it will show
- Now, We have to deploy our smart contract on Polygon Network. For that, we have to connect to web3 world, this can be done by using any of the services like Metamask, Brave, Portis etc. We will be using Metamask. Please follow this tutorial to setup a Metamask Account.
- Open Metamask and select Custom RPC from the networks dropdown
Put in a Network name - “Matic Mumbai Testnet”
In URL field you can add the URL as "https://rpc-mumbai.maticvigil.com"
Enter the Chain ID: 80001
(Optional Fields) Symbol: "maticmum" and Block Explorer URL: "https://mumbai.polygonscan.com/"
Go ahead and click save
Copy your address from Metamask
Head over to Faucet and request test ether - you will need this pay for gas on Matic. Select 'Mumbai' as the network and 'MATIC Token' as the token in the faucet
Now, let's Deploy the Smart Contract on Matic Network
Select Injected Web3 in the Environment dropdown and your contract
- Accept the Connection Request!
- Once Metamask is connected to Remix, the ‘Deploy’ transaction would generate another metamask popup that requires transaction confirmation.
Congratulations! You have successfully deployed HelloWorld Smart Contract. Now you can interact with the Smart Contract. Check the deployment status here: https://mumbai.polygonscan.com/.
Verifying your Contracts on PolygonScan
The first and foremost step is to flatten the solidity contract into a single file.
Flatten your solidity contract
Flatten using command
sol-merger \"./contracts/*.sol\" ./build
Verifying on Polygonscan
Navigate to your contract's polygonscan page and then click verify and publish
Solidity (Single File)in compiler type
- Select appropriate compiler version
- Choose the license type of your contract
Onto the next section, paste your flattended contract here.
If you had enabled optimization then adjust the
optimization section accordingly.
Constructor arguments should have been filled in automatically, if not, they can be retrieved from the trailing bytes of the deployment transaction, they resemble something like
That's it, you are done. 🎉