How to call methods of Ethereum Smart-Contracts from WordPress with MetaMask, Web3 and Javascript

First you must create and deploy a SMART-CONTRACT in the Ethereum Test Net, you can follow these instructions:

• Creating my first Ethereum Smart-Contract in Test net
• Creating MrAddon token in Ethereum

This post is based in the information of the previous post:

• Javascript development to interact with Ethereum Smart-Contracts

To start, we have hosted a WordPress site and we want to create a “button” to interact with an Ethereum Smart-contract.

In this case, we will create a button to call the method “transfer”, it will transfer 88,88 tokens through MetaMask (it’s a Google Chrome Plugin). The code is inserted in a page of WordPress.

Then, we can start to create the WordPress page and insert the Javascript code.

The code:

<script src="http://rawgit.com/ethereum/web3.js/0.16.0/dist/web3.min.js"></script>
<script src="https://cdn.jsdelivr.net/npm/ethjs@0.3.0/dist/ethjs.min.js"></script>
<script>
    window.addEventListener('load', function() {
    // Check if Web3 has been injected by the browser:
    if (typeof web3 !== 'undefined') {
        // You have a web3 browser! Continue below!
        startApp(web3);
        //alert("Web3");
    } else {
        //alert("No hay web3");
        // Warn the user that they need to get a web3 browser
        // Or install MetaMask, maybe with a nice graphic.
    }
})
const abi = [{
    "constant": false,
    "inputs": [
        {
            "name": "_to",
            "type": "address"
        },
        {
            "name": "_value",
            "type": "uint256"
        }
    ],
    "name": "transfer",
    "outputs": [
        {
            "name": "success",
            "type": "bool"
        }
    ],
    "payable": false,
    "type": "function"
}]
const contract_address = '0xf035755df96ad968a7ad52c968dbe86d52927f5b'
const etherValue = web3.toWei(10, 'ether');
var address = '0x91612055A68aD74A6e756615941Ac59e9220A940'
function startApp(web3) {
    //alert("entro");
    const eth = new Eth(web3.currentProvider)
    const token = eth.contract(abi).at(contract_address);
    listenForClicks(token,web3)
    //alert("llego");
}
function listenForClicks (miniToken, web3) {
    var button = document.querySelector('button.transferFunds')
    web3.eth.getAccounts(function(err, accounts) { console.log(accounts); address = accounts.toString(); })
    button.addEventListener('click', function() {
        miniToken.transfer(contract_address, '88888888888888888888', { from: address })
            .then(function (txHash) {
            console.log('Transaction sent')
            console.dir(txHash)
            waitForTxToBeMined(txHash)
        })
            .catch(console.error)
    })
}
async function waitForTxToBeMined (txHash) {
    let txReceipt
    while (!txReceipt) {
        try {
            txReceipt = await eth.getTransactionReceipt(txHash)
        } catch (err) {
            return indicateFailure(err)
        }
    }
    indicateSuccess()
}
</script>
<button class="transferFunds">Send Money!</button>

Then we can save the page and test it! (Remember to change the contract address and the amount of tokens to transfer!.. also to connect the MetaMask plugin!)

Once we submit the transaction, we will see in Etherscan the result of calling the method “transfer“.

And we will see “Transaction sent” in the Console log!

Post by MrAddon