how to dynamically reload a script?

Loading code from other files is done with require. However, once you've require'd a file, requiring it again will not load the file from disk again, but from a memory-cache which Node maintains. To reload the file again, you'll need to remove the cache-entry for your file before you call require on it again.

Say your file is called /some/path/file.js:

// Delete cache entry to make sure the file is re-read from disk.
delete require.cache['/some/path/file.js'];
// Load function from file.
var func = require('/some/path/file.js').func;

The file containing the function would look something like this:

module.exports = {
  func : function() { /* this is your function */ }
};

In addition to @robertklep's answer, here is a solution for any path:

const path = require('path');

var lib_path = './test' // <-- relative or absolute path                                                                  
var file = require(lib_path);

const reset_cache = (file_path) => {
    var p = path.resolve(file_path);
    const EXTENTION = '.js';
    delete require.cache[p.endsWith(EXTENTION) ? p : p + EXTENTION];
}

// ... lib changed                                                                                                             

reset_cache(lib_path);
file = require(lib_path); // file changed

Unfortunately, all dependencies of the reloaded file didn't reload too.

Also, you can use the clear-module package:

const clear_module = require('clear-module');

require('./foo');
// ... modify
clear_module('./foo');
require('./foo');

It can clear all modules and handle regexp.