Node.js: fs.existsSync doesn’t work on Heroku

I have a Heroku app using Node.js and Express, and I want to determine whether or not a certain file exists. However, it seems like the file is never found. I have the following path:

app.get('/sims/:sim_name', (req, res) => {
    var simName = req.params.sim_name; // get the name of the requested sim from the URL
    // if it exists, render it
    if (fs.existsSync(`pages/sims/${simName}.ejs`)) 
        res.render(`pages/sims/${simName}`);
    // otherwise, show an error message
    else
        res.send("Sorry, the page you requested does not exist.");
});

The directory structure of my project looks like this:

.
├── Procfile
├── README.md
├── app.json
├── index.js
├── node_modules
│   ├── so many node_modues...
├── package-lock.json
├── package.json
├── public
│   ├── images
│   │   └── ...
│   ├── lang-logo.png
│   ├── node.svg
│   ├── scripts
│   │   └── ...
│   ├── stylesheets
│   │   ├── ...
│   └── test.html
├── test.js
└── views
    ├── pages
    │   ├── index.ejs
    │   ├── sims
    │   │   └── EField.ejs
    └── partials
        ├── header.ejs
        └── nav.ejs

I am doing something wrong here? Or is this a Heroku issue?

Answer

Ok, I needed to change pages/sims/${simName}.ejs to views/pages/sims/${simName}.ejs.

I had previously tried /views/pages/sims/${simName}.ejs, which didn’t work because of how the file paths work in Heroku.

I also added braces, as per the suggestion of @UserToday (although this wasn’t necessary).