Anatomy of a Contract

Anatomy of an Ethereum Contract

In this case we'll look at a simple storage program.

Solidity Code

contract SimpleStorage {
    uint storedData;
    function set(uint x) {
        storedData = x;
    }
    function get() constant returns (uint retVal) {
        return storedData;
    }
}

ABI

[
  {
    "constant": false,
    "inputs": [
      {
        "name": "x",
        "type": "uint256"
      }
    ],
    "name": "set",
    "outputs": [],
    "type": "function"
  },
  {
    "constant": true,
    "inputs": [],
    "name": "get",
    "outputs": [
      {
        "name": "retVal",
        "type": "uint256"
      }
    ],
    "type": "function"
  }
]

Byte Code

Here is the Ethereum Byte code for this contract: 6060604052603b8060116000396000f300606060405260e060020a600035046360fe47b1811460245780636d4ce63c14602e575b005b6004356000556022565b6000546060908152602090f3

Complete Javascript Code

var abi = [
        {
            "constant": false,
            "inputs": [
                {
                    "name": "x",
                    "type": "uint256"
                }
            ],
            "name": "set",
            "outputs": [],
            "type": "function"
        },
        {
            "constant": true,
            "inputs": [],
            "name": "get",
            "outputs": [
                {
                    "name": "retVal",
                    "type": "uint256"
                }
            ],
            "type": "function"
        }
    ],
    code = '6060604052603b8060116000396000f300606060405260e060020a600035046360fe47b1811460245780636d4ce63c14602e575b005b6004356000556022565b6000546060908152602090f3',
    deployTransactionObject = {
        from: web3.eth.accounts[0],
        gas: 300000,
        data: code,
    },
    setTransactionObject = {
        from: web3.eth.accounts[0],
        gas: 300000,
    };

Setup Contract in JS

Setup the SimpleStorage Contract Object in JS

var SimpleStorage = web3.eth.contract(abi);

Deploy

Deploy a new SimpleStorage contract to the Ethereum blockchain

SimpleStorage.new(deployTransactionObject, function(err, contract){
    if(err)
        console.log('There was an error deploying your SimpleStorage contract on the Blockchain: ', err);

    if(!err) {
        if(!contract.address) {
            console.log('Your transaction was posted to the Ethereum blockchain with this hash identifier: ', contract.transactionHash);
        } else {
            console.log('Your contract was deployed to this address on the blockchain: ', contract.address);
        }
    }
});

Accessing Storage

Once you have deployed your SimpleStorage contract, use the address provided below as the .at address to set up a SimpleStorage Contract Instance

var contractInstance = SimpleStorage.at('0x7de20ad122e172d75086abe4df51841851f2019c');

Set Stored Value

Set Stored Value in your SimpleStorage contract on the Ethereum blockchain

contractInstance.set.sendTransaction(456, setTransactionObject, function(err, result){
    if(err)
        console.log('Error Saving Data on SimpleStorage: ', err);

    if(!err)
        console.log('Transaction Hash: ', result);
});

Retrieve Stored Value

Get the stored value from your SimpleStorage contract on the Ethereum blockchain

contractInstance.get.call(function(err, result){
    if(err)
        console.log('Error Calling Contract', err);
    
    if(!err)
        console.log('Stored Value: ', result);
});

For more MeteorJS-based decentralized applications please check out https://github.com/SilentCicero?tab=repositories.