Why does accessing variables declared without `var` work without having to use `require` in other files?

Question

Here's an example

$ cat main.js
App = {
  version : 1.1
};
require('./mymod.js');

$ cat mymod.js
console.log(App.version);

$ node main.js
1.1

Note how I declared App in main.js without var. This allowed me to access App from mymod.js without having to call require. If I declare App with a var, this won't work.

I want to understand why this happens? Is it the intended behaviour for node.js or a bug? Is this behavior consistent with ECMAScript or CommonJS standards?

This trick gives a powerful mechanism to circumvent the require module system of node.js. In every file define your objects and add them to the top level App namespace. Your code in other files will be automatically have access to those objects. Did I miss something?

Answer 1

If you assign a variable without using var, it is automatically a global variable. That's just the way JavaScript works. If you put 'use strict'; (quotes required) at the top of your js file, this becomes an error instead.

Answer 2

All has to do with local scope vs global scope.

You can even do this (which is much neater):

app.js:

exports = {
  version : 1.1
}; 

---

main.js:

var App = require('./app.js');
console.log(App.version);