Express res.sendfile throwing forbidden error

I believe it's because of the relative path; the "../" is considered malicious. Resolve the local path first, then call res.sendfile. You can resolve the path with path.resolve beforehand.

var path = require('path');
res.sendFile(path.resolve('temp/index.html'));

The Express documentation suggests doing it a different way, and in my opinion it makes more sense later than the current solution.

res.sendFile('index.html', {root: './temp'});

The root option seems to set ./ as the root directory of your project. So I cannot fully tell where you file is in relation to the project root, but if your temp folder is there, you can set ./temp as the root for the file you're sending.

Also, you can use path.join

const path = require("path");

router.get("/", (req, res) => {
  let indexPath = path.join(__dirname, "../public/index.html");
  res.sendFile(indexPath);
});

This answer gathers together the info from the other answers/comments.

It depends whether you want to include something relative to the process working directory (cwd) or the file directory. Both use the path.resolve function (put var path = require('path') at the top of the file.

• relative to cwd: path.resolve('../../some/path/to/file.txt');
• relative to file: path.resolve(__dirname+'../../some/path/to/file.txt');

From reading the link from @Joe's comment, it sounds like relative paths are a security risk if you accept user input for the path (e.g. sendfile('../.ssh/id_rsa') might be a hacker's first try).