问如何在一个范围内获取var的值并在另一个文件中使用它

EN

//this works, findUser would log the user id
var findUser;
router.get('/dashboard', (req,res)=>{
  findUser = req.user.id;
//findUser = req.session.passport.user;
 console.log(findUser);
res.send(req.user);
});
// this does not work, returns undefined
     users js file
  // module.exports.findUser;
   module.exports.findUser = req.user.id;
    // post.js file
   var sourceFile = require('./users');
   console.log(sourceFile.findUser);