A ScratchX extension for connecting to the Ethereum blockchain and ERC20 token contracts.
Scratch does not support loading custom extensions so the ScratchX Editor is used instead.
The JavaScript code for the Ethereum extension is in ethBlock.js. This can be loaded into SctatchX in two ways:
- From a local file
Clone this repository to your local machine using
git clone https://github.com/naddison36/eth-scratch.git
cd eth-scratch
Open the ScratchX Editor (you will have to allow the Flash plug-in), select the Scripts tab and then select More Blocks. Then hold the control button on the keyboard and click the Load Experimental Extension button.
- From the web
In theory, you can load from an external url but I haven't gotten that to work.
Once loaded, the extension has a number of report and command blocks to get data from the Ethereum blockchain or send signed transaction via a browser wallet like MetaMask.
The command blocks should pop up a browser wallet to sign the transaction and send them onto the Ethereum network. Here's an example for signing a token transfer using MetaMask. The transaction from address, gas price and gas limit are all set in the browser wallet.
All the addresses need to be prefixed with 0x.
| Block | Notes |
|---|---|
| ether balance of address %s | gets the ether balance of an address which can be an externally owned account or a contract |
| send %s ether to address %s | sends a number of ether to an address |
| transfer %s tokens to address %s of contract address %s | assumes a contract with an ERC20 transfer function exists at the contract address |
| transfer from address %s to address %s %s tokens for contract %s | assumes a contract with an ERC20 transferFrom function exists at the contract address |
| approve address %s to spend %s tokens for contract %s | assumes a contract with an ERC20 approve function exists at the contract address |
| mint %s tokens to address %s for contract %s | assumes a contract with an Open Zeppelin mint function exists at the contract address. |
| deploy token contract for %s | The name parameter is used to set both the token symbol and name |
| token balance of address %s for contract %s | assumes a contract with an ERC20 balanceOf function exists at the contract address |
| allowance of owner address %s to spender address %s | assumes a contract with an ERC20 allowance function exists at the contract address |
| token %m of token contract %s | get the name, symbol or decimals properties of the deployed contract |
| network name | returns the name of the network the browser wallet it connected to. This is useful for testing connectivity. |
| when transaction on contract %s | Not currently implemented |
There is no error handling with ScratchX extensions so the best that can be done is logging errors in the browser's JavaScript console.
Ethereum is a decentralized platform for applications that run exactly as programmed without any chance of fraud, censorship or third-party interference.
GameToken is an ERC20 compliant, token contract to test the integration between the Scratch extension and a token contract. Note the constructor only takes one string parameter which is used to set the symbol and name properties of the contract.
The deploy block command will deploy the GameToken contract that was compiled using Solidity 0.4.25 (0.4.25+commit.59dbf8f1.Emscripten.clang) with optimization enabled.
Remix is the easiest way to compile, deploy and interact with Ethereum smart contracts.
The GameToken contract is dependent on the Open Zeppelin smart contract library. Run the following to install the Open Zeppelin
npm install openzeppelin-solidity
In order to be able to load all the dependent Open Zeppelin contracts in Remix, remixd can be used to connect Remix running in the browser to the local filesystem where the GameToken and dependent Open Zeppelin files are found. To install and run remixd
npm install -g remixd
remixd -s <your full path>/eth-scratch --remix-ide https://remix.ethereum.org
See Access your local filesystem by using RemixD for more details.
In order to connect Remix to MetaMask, the Enable Personal Mode setting in Remix needs to be disabled.
Your Ethereum account will need some Ether in order to deploy the GameToken contract and send transactions. The MetaMask Ether Faucet can be used to get Ether for the public test networks like Ropsten. For mainnet, you'll have to purchase Ether from a broker or exchange.
Scratch 3.0 will be released on 2 January 2019. The update from Scratch 2.0 to 3.0 includes extensions so the old ScratchX site will be unsupported. Once Scratch 3.0 has been released, this ScratchX extension will be upgraded to Scratch 3.0. See With the upcoming Scratch 3.0, the extension structure has been completely revamped for a preview of the changes. Also see Scratch 3.0 Extensions Specification on their GitHub wiki.