promisify an entire nodejs module using util.promisify

promisifyAll.js

function promisifyAll(module, callbackParameterName) {
	const util = require('util')

	function isFunction(f) {
		return f && Object.prototype.toString.call(f) === '[object Function]'
	}

	if (!callbackParameterName) callbackParameterName = 'callback'

	Object.keys(module)
		.forEach(key => {
			if (!isFunction(module[key])) return
			let args = module[key].toString().match(/function\s.*?\(([^)]*)\)/)[1].split(',')
				.map(arg => arg.replace(/\/\*.*\*\//, '').trim())
				.filter(arg => arg)
			if (args.length == 0 || args[args.length - 1] != callbackParameterName) return
			module[key] = util.promisify(module[key])
		})

	return module
}

// async / await example

const fs = promisifyAll(require('fs'))

;(async function() {
	try {
		await fs.writeFile('hello.txt', 'Hello world!')
	}
	catch (e) {
		console.error(e)
	}
})()