//student.js

function add(student) {
   console.log(student);
}

exports.add = add;

.................................................................................（分割线）

//teacher.js

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

function add(teacher) {
   console.log(teacher);
}

student.add('小明');

add('张老师');

而控制台的错误提示：

TypeError: student.add is not a function
   at Object. (D:\LearnTools\Sublime Text 3x64\Project\Nodejs-test\s
chool2\teacher.js:9:9)
   at Module._compile (module.js:413:34)
   at Object.Module._extensions..js (module.js:422:10)
   at Module.load (module.js:357:32)
   at Function.Module._load (module.js:314:12)
   at Function.Module.runMain (module.js:447:10)
   at startup (node.js:146:18)
   at node.js:404:3