thebergamo/contents.js

## contents.js
console.log('lolololo');

## index.html
<html>
  <head><!-- awesome head here --></head>

  <body> <!--awesome body here -->

    <replace src="./contents.js" />
  </body>

</html>

## replacer.js
'use strict';

const Promise = require('bluebird');
const fs = Promise.promisifyAll(require('fs'));

fs.readFileAsync('./index.html')
  .then(function(data) {
    // match the replace tags
    const regex = /<replace src="(.+)" \/>/;

    // Transform data Buffer to string.
    let strData = data.toString();
    const fileInfo = strData.match(regex);

    return [strData, fileInfo, fs.readFileAsync(fileInfo[1])];
  })
  .spread(function(html, fileInfo, contents) {
    // Set String template to replace
    const templateStr = '<script>\n' + contents + '</script>';

    return fs.writeFileAsync('index.new.html', html.replace(fileInfo[0], templateStr));
  })
  .then(function () {
    console.log('file writed in index.new.html');
  })
  .catch(function (err) {
    throw err;
  });
	<html>
	<head><!-- awesome head here --></head>

	<body> <!--awesome body here -->

	<replace src="./contents.js" />
	</body>

	</html>
	'use strict';

	const Promise = require('bluebird');
	const fs = Promise.promisifyAll(require('fs'));

	fs.readFileAsync('./index.html')
	.then(function(data) {
	// match the replace tags
	const regex = /<replace src="(.+)" \/>/;

	// Transform data Buffer to string.
	let strData = data.toString();
	const fileInfo = strData.match(regex);

	return [strData, fileInfo, fs.readFileAsync(fileInfo[1])];
	})
	.spread(function(html, fileInfo, contents) {
	// Set String template to replace
	const templateStr = '<script>\n' + contents + '</script>';

	return fs.writeFileAsync('index.new.html', html.replace(fileInfo[0], templateStr));
	})
	.then(function () {
	console.log('file writed in index.new.html');
	})
	.catch(function (err) {
	throw err;
	});