Load and execute external js file in node.js with access to local variables?

Just do a require('./yourfile.js');

Declare all the variables that you want outside access as global variables. So instead of

var a = "hello" it will be

GLOBAL.a="hello" or just

a = "hello"

This is obviously bad. You don't want to be polluting the global scope. Instead the suggest method is to export your functions/variables.

If you want the MVC pattern take a look at Geddy.

If you are planning to load an external javascript file's functions or objects, load on this context using the following code – note the runInThisContext method:

var vm = require("vm");
var fs = require("fs");

var data = fs.readFileSync('./externalfile.js');
const script = new vm.Script(data);
script.runInThisContext();

// here you can use externalfile's functions or objects as if they were instantiated here. They have been added to this context. 

If you are writing code for Node, using Node modules as described by Ivan is without a doubt the way to go.

However, if you need to load JavaScript that has already been written and isn't aware of node, the vm module is the way to go (and definitely preferable to eval).

For example, here is my execfile module, which evaluates the script at path in either context or the global context:

var vm = require("vm");
var fs = require("fs");
module.exports = function(path, context) {
  var data = fs.readFileSync(path);
  vm.runInNewContext(data, context, path);
}

Also note: modules loaded with require(…) don't have access to the global context.

You need to understand CommonJS, which is a pattern to define modules. You shouldn't abuse GLOBAL scope that's always a bad thing to do, instead you can use the 'exports' token, like this:

// circle.js

var PI = 3.14; // PI will not be accessible from outside this module

exports.area = function (r) {
  return PI * r * r;
};

exports.circumference = function (r) {
  return 2 * PI * r;
};

And the client code that will use our module:

// client.js

var circle = require('./circle');
console.log( 'The area of a circle of radius 4 is '
           + circle.area(4));

This code was extracted from node.js documentation API:

http://nodejs.org/docs/v0.3.2/api/modules.html

Also, if you want to use something like Rails or Sinatra, I recommend Express (I couldn't post the URL, shame on Stack Overflow!)