Object methods are unavailable after including with require

I'm working through Node.js module, but I'm stuck on how to export a prototype in a way that makes the methods accessible.

For example, take the following code:

var myobj = function(param) {
  this.test = 'a test';
  return this.param = param;
};

myobj.prototype = {
  indexpage: function() {
    console.log(this.test);
    return console.log(this.param);
  }
};

var mo = new myobj('hello world!');
mo.indexpage();

My results are as expected:

a test
hello world!

If I take the same code and place it in another file with module.exports:

somefile.js

var myobj = function(param) {
  this.test = 'a test';
  return this.param = param;
};

myobj.prototype = {
  indexpage: function() {
    console.log(this.test);
    return console.log(this.param);
  }
};

// the only line that is different
module.exports = myobj;

app.js code

var MyObj = require('myobj.js');
var mo = new MyObj('hello world!');
mo.indexpage();

Now I get TypeError: Object #<Object> has no method 'indexpage'

Where am I going wrong? I've been working on this single issue for hours; my basic grasp of javascript isn't helping me figure out this issue any more than searching forums.