parse.com - Parse Javascript - Relation is not a function -

i'm trying understand how relation works , did wrote simple script:

var parse = require('parse/node');  parse.initialize('myappid'); parse.serverurl = 'http://localhost:1337/parse';  var userquery = new parse.query(parse.user); userquery.equalto('username', 'the_username');  userquery.find()     .then(user => {         return user;     })     .then(user => {         var systems = parse.object.extend("systems");         var systemquery = new parse.query(systems);         systemquery.equalto('customer', 'mycustomer');          systemquery.find()             .then(system => {                 var relation = user.relation('systems_ref'); // here relation not func                 relation.add(system);                 console.log('adding relation');                  user.save()                     .then(response => console.log('user saved'))                     .catch(error => console.log('error saving', error));             }).catch(error => console.log('error find system', error));     }); 

but in line try user.relation have error "relation not function".

i have others example on how create relation, dont see difference in code...

i have user (that sublcass of parseobject), , on i'm trying access relation method...

you may use follows: add post user javascript sdk:
var user = parse.user.current();
var relation = user.relation("posts");
relation.add(post);
user.save();