// index.js

        var classes = require('./klass');

//student.js

        function add(student){

             console.log("add student:"+student);

        }

        exports.add=add;

//teacher.js 

        function add2(teacher){

             console.log('woshishei');    

        }

        exports.add2=add2;

//klass.js

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

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

            function add(teacher,students){

                 student.add(students);

                 console.log(teacher);

                 teacher.add2(teacher);

        };

        exports.add = add;