NodeJs - Retrieve user infor from JWT token?

First of all, it is a good practice to use Passport middleware for user authorization handling. It takes all the dirty job of parsing your request and also provides many authorization options. Now for your Node.js code. You need to verify and parse the passed token with jwt methods and then find the user by id extracted from the token:

exports.me = function(req,res){
    if (req.headers && req.headers.authorization) {
        var authorization = req.headers.authorization.split(' ')[1],
            decoded;
        try {
            decoded = jwt.verify(authorization, secret.secretToken);
        } catch (e) {
            return res.status(401).send('unauthorized');
        }
        var userId = decoded.id;
        // Fetch the user by id 
        User.findOne({_id: userId}).then(function(user){
            // Do something with the user
            return res.send(200);
        });
    }
    return res.send(500);
}

Find a token from request data:

const usertoken = req.headers.authorization;
const token = usertoken.split(' ');
const decoded = jwt.verify(token[1], 'secret-key');
console.log(decoded);

Your are calling the function UserService.me with two callbacks, although the function does not accept any arguments. What I think you want to do is:

$scope.me = function() {
    UserService.me().then(function(res) {
      $scope.myDetails = res;
    }, function() {
      console.log('Failed to fetch details');
      $rootScope.error = 'Failed to fetch details';
    });
  };

Also, note that the $http methods return a response object. Make sure that what you want is not a $scope.myDetails = res.data

And in your Users.js file, you are using the variable headers.authorization directly, whereas it should be req.header.authorization:

var authorization = req.headers.authorization;