create bitcoin wallet, make a transaction on bitcoin network using bitcoinjs-lib and blockcypher

bitcoin.js

var request = require('request');
const bitcoin = require('bitcoinjs-lib');
var buffer = require('buffer');
const bitcoinNetwork = bitcoin.networks.testnet;

var rootUrl = "https://api.blockcypher.com/v1/btc/test3";


//create wallets
const TestNet = bitcoin.networks.testnet3;
let keyPair = bitcoin.ECPair.makeRandom({ network: TestNet });
let publicKey = keyPair.publicKey.toString('hex');
let {address} = bitcoin.payments.p2pkh({ pubkey: keyPair.publicKey });
let wif = keyPair.toWIF();
var privateKey   = bitcoin.ECPair.fromWIF(wif, TestNet);
console.log("Public: " + publicKey + " \nPrivate: " + privateKey + " \nAddress: " + address + " \nWIF: " + wif);

var source = {
  public  : <pub_key>,
  address : <addr>,
  wif : <wif>,
  dest: <dest_addr>
}

var price_per_byte = 40;

//get balance of a wallet
request.get(rootUrl + "/addrs/" + source.address + "/balance",(error, response, body) => {
    	if(body.error || JSON.parse(body).errors){
    		if(body.error)
    			console.log(body.error);
    		else console.log(JSON.parse(body).errors[0].error);
    	} else {
    		console.log(body);
   			let parsed_body = JSON.parse(body);
   			let balance = parsed_body.balance;
    		let unconfirmed_balance = parsed_body.unconfirmed_balance;
    		if(unconfirmed_balance < 0)
    			balance = balance + unconfirmed_balance;
    		console.log("balance : " + balance);
    	}
    }
);


// send token from one wallet to another
var key   = bitcoin.ECPair.fromWIF(source.wif, bitcoinNetwork);
request.get(rootUrl + "/addrs/" + source.address + "?unspentOnly=true",(error, response, body) => {
    	if(body.error || JSON.parse(body).errors){
    		if(body.error)
    			console.log(body.error);
    		else console.log(JSON.parse(body).errors[0].error);
    	} else {
    		let parsed_body = JSON.parse(body);
   			let balance = parsed_body.balance;
    		let unconfirmed_balance = parsed_body.unconfirmed_balance;
    		if(unconfirmed_balance < 0)
    			balance = balance + unconfirmed_balance;
    		var tx = new bitcoin.TransactionBuilder(bitcoinNetwork);
    		let txs = JSON.parse(body).txrefs;
    		if (balance > 0 && txs) {
				txs.forEach(function(txn) {
					console.log(txn);
					tx.addInput(txn.tx_hash, txn.tx_output_n);
				});

				request.get("https://bitcoinfees.earn.com/api/v1/fees/recommended",(error, response, body) => {
					try{
						if(!error)
							price_per_byte = JSON.parse(body).halfHourFee;
					} catch(ex){
						console.log("unable to find fee, setting default as 10satoshi per byte");
					}
					console.log("price_per_byte : " + price_per_byte);
					let fee = (txs.length * 148 + 1 * 34 + 10) * price_per_byte;//1 is the no of outputs
					let amount_to_transfer = balance - fee;
					console.log("fee : " + fee +"\nBalance : "+amount_to_transfer);
					tx.addOutput(source.dest, amount_to_transfer);
					let txn_no = txs.length;
					while(txn_no > 0){
						tx.sign(txn_no-1, key);
						txn_no--;
					}
					let tx_hex = tx.build().toHex();
					request.post(rootUrl + "/txs/push",{json :{tx: tx_hex}}, (error, response, body) => {
		    			if(body.error)
		    				console.log(body.error);
		    			 else 
		    				console.log(body.tx.hash);
		    		});
	    		});
			} else console.log("Not enough balance : " + balance);
    	}
    }
);