How to get absolute file path of a file inside a folder on another folder using NodeJS?

I want to view index.html file inside client on the controllerClient.js file inside controller folder using sendFile option. It is working fine on my localhost using the following code but when i try to host it on vercel it show the following error

Error: ENOENT: no such file or directory, stat '/var/task/client/index.html'

controllerClient.js Code

const viewHome = async (req, res) => {
     res.sendFile("/client/index.html", { root: "." });
};

How can I make the code better to make it useful for multi platform ?

You can use path module to join the current path with __dirname variable which is given by node. __dirname returns the current directory.

const path = require('path');
const express = require('express');
const app = express();

app.use(express.static(path.join(__dirname, 'public')));

Public directory here are the front end files which are sent to the browser. In your case it will be the client directory.

When using

res.send('index');

above can be used with only the view name instead of full path.