use this to get a fields value from js

var Users = new openerp.Model('res.users');
Users.query(['name', 'login', 'user_email', 'signature'])
     .filter([['active', '=', true], ['company_id', '=', main_company]])
     .limit(15)
     .all().then(function (users) {
    // do work with users records, you can access only fields said in query
     for(i in users){
         console.log(i.name)
     }
 });

please refer this link

However a call to py function or model is done only after all js functions are executed.
if you need to use this variable, you should call the js function inside .then(function (users){ and pass your values

for example

var self = this
var Users = new openerp.Model('res.users');
Users.query(['name', 'login', 'user_email', 'signature'])
     .filter([['active', '=', true], ['company_id', '=', main_company]])
     .limit(15)
     .all().then(function (users) {
    // do work with users records, you can access only fields said in query
     for(i in users){
         console.log(i.name)
         self.your_function(sample_var)
     }
 });