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Buying An Image -- Sending Transactions

We can read an image, so now let’s color each pixel on the blockchain.

What we’re going to do is iterate over each pixel and send a transaction for each pixel we want to color. Of course, this can be a lot of transactions if the image is large. But the idea is that someone is purchasing a scarce pixel, for a long period of time, so it’s not that big of a deal if it takes a while to buy the whole image.

Connecting to Web3

The first thing we need to do is connect to our web3 node:

const Web3 = require('web3');
const web3 = new Web3();

  new web3.providers.HttpProvider('http://localhost:8545')

Here I’m using the HttpProvider, but it’s worth looking into the IpcProvider, too.

Getting a handle to the contract

Next we need a handle to our contract. We do this, like we have before, by loading the ABI and looking up the contract’s deployed address.

const abi = require('../src/MillionEtherPage.abi.json');
const mepAddress =
const mep = new web3.eth.Contract(abi, mepAddress);

Because we’re sending transactions, we’ll also need the sending account address. Normally, you’d configure this as an environment variable or command-line argument, but we can hardcode it for now.

const fromAccount =

Now that we have the contract, when we loop over each pixel, instead of logging it, we want to call the colorPixel method on the contract to send a transaction:


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