Before you start building your program, make sure you have Node.js and NPM (short for Node Package Manager) installed.

In order to create an OP_RETURN transaction, we can use one of the many available bitcoin APIs, such as:

• bitcore (https://bitcore.io/)
• php-OP_RETURN (https://github.com/coinspark/php-OP_RETURN)
• python-OP_RETURN (https://github.com/coinspark/python-OP_RETURN)

In our example, we will use a JavaScript library called bitcoinjs-lib written for Node.js. We install the corresponding package as follows:

npm install bitcoinjs-lib --save

In the example code, we will submit requests using Node.js and the request package to access the API. Therefore, we install the following modules:

npm install request --save
npm install request-promise --save

Similar to the first method, we will use the first address and its corresponding private key generated by Electrum to send a raw transaction carrying a hello world message programmatically.