node.js require issue

I am implement following this.

//to_s.js
(function(){
String.prototype.to_s = function(){
        var str = this.toString();
        var convert = function(s){
            return eval(s);
        };

        while(/#{(\w+)}/.test(str)){

            // bad  because I use eval...

            var matchStr =RegExp.$1;

            var str = str.replace(/#{(\w+)}/,convert(matchStr));

        }
        return str;
    };
})();

module.exports = String.prototype.to_s;


// test/to_s_test.js

require("./../to_s");

var name = 33;

"hello #{name}".to_s();

I run to_s_test.js, but it happend error that 'name is undefined'.But I don't know why it happen.But change 'var name = 33' to name = 33 , It works... Do you have any idea? Thanks in advance.