You don't escape the public directory with express.static(). That is done for security reasons so people can't make up URLs and go poking around your server hard drive.
Instead, you need to make a new route for that script file. If it's a single file and it's in a node_modules directory below where your source file is, you can make just a simple single route:
app.get("/myscript.js", function(req, res) {
res.sendFile(path.join(__dirname, "node_modules/someModule/somescript.js"));
});
Note in this example that the URL you use does not have to be the same as the file's actual name. Unlike with express.static(), they are independent when making a custom route like this so you can make the URL filename be whatever you want as long as it doesn't conflict with other routes you have.
If there are multiple files in that same directory that you want public, but you don't want others in that directory hierarchy to be public, then you can't really use another express.static() to only target a couple files in that directory so you'd either have to move the public files to their own directory or make an individual route for each file.
Here are some other examples:
How to include scripts located inside the node_modules folder?
How to add static file from `node_modules` after declare the `public` as static in express?
