Require a file within itself in node.js

You can totally do it. Try this, for instance (in a file named a.js):

exports.foo = 'foo';

var a = require('./a');

console.log(a);

exports.bar = 'bar';

console.log(a);

At the point where require executes, it will return the module a as it exists at the point where require runs so the field foo will be defined but not bar.

There's no point to doing this though. You use require to bring into your current scope an object which would otherwise not be available (namely, a module). But you don't need to do this to access the module you are currently in: it is already fully available.

The code above works because Node has rules to handle cyclic dependencies. And here you have a module which is cyclicly dependent on itself. Rather than go into an infinite loop of requires, Node has require return the module as built up to that point: a partial module. And the modules in a cyclic dependency have to be designed to handle the fact that they may get partial modules.

Cyclic dependencies are to be avoided as much as possible. Most of the time this means refactoring the modules to avoid the mutual dependency by moving functionality into one or more new modules.

So, again, the best practice is to not do this in the first place.