Insert <script> block into template.html BEFORE </body> tag (Node.js)

insertScript.js

const fsp = require('fs').promises

const readFilePath = './template.html'
const writeFilePath = './index.html'

const block = `
	<script>
		const eventSource = new EventSource('http://localhost:3000/subscribe')
		eventSource.onerror = () => { console.log('Error with live-server') }
		eventSource.onmessage = () => { window.location.reload() }
	</script>
`

fsp
	.readFile(readFilePath, 'utf-8')
	.then(data => data.replace(/\<\/body>/, block + '$&'))
	.then(data => fsp.writeFile(writeFilePath, data, 'utf-8'))
	.catch(err => console.error(err))