Why is it impossible to get and give module.exports in one file?

Question

Node.js

There is a module to which, when connected, a function / variable is passed, for example, like this:
myModule = require('./mymodule')(param);
In the module, the variable is received like this:

var param;
module.exports = function(item){
  param = item;
}

And it works, now the param from the external file is available in myModule.
But at the same time, it is impossible to transfer anything from myModule. If I do this in myModule:

echo = function(){
  console.log('ok');
}
module.exports.echo = echo;

And in an external file like this:
myModule.echo();
That will give an error "Cannot read property 'echo' of undefined".
What can be done?

Answer 1

mymodule.js

var param = "param";

module.exports = function(item){
    var self = this;
    param = item;
    self.echo = function(){
        console.log(param);
    }
    return {
        echo: self.echo
    }
}

var myModule = require('./mymodule')("newparam");
myModule.echo();