How to make parse find/save operations synchronous?

We are writing server code in nodejs and using Parse javascript sdk. Often we need to fetch or update various Parse objects. For example, fetch a user with username 'Example'.

  function fetchUser(username)
  {
      var User = Parse.Object.extend("User");
      var query = new Parse.Query("User");
      query.equalTo("username",username);

      query.first({
        success: function(results) {
        console.log("Successfully retrieved " + results.length + " scores.");
        return results;
      },
      error: function(error) {
        console.log("Error: " + error.code + " " + error.message);
      }
     });
  }

This function might be called by some other function:

function test()
{
    var user = fetchUser("example");
    console.log(user); // would often print undefined
    return user;
}

function top()
{
    // some code
    var user = test();
    //some code
}

// and the function top() mmight be called by some other functions

The problem is that I would get undefined results because the find/first operations runs asynchronously. Is there any way to ensure that fetchUser() function returns only when the find/first operation is successful/complete?

NodeJs is single threaded, so we should not block process.

in your case you have two options 1. passing callback 2. using Promise library (https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise)

Ex 1: passing callback

    function fetchUser(username, callback)
  {
      var User = Parse.Object.extend("User");
      var query = new Parse.Query("User");
      query.equalTo("username",username);

      query.first({
        success: function(results) {
        console.log("Successfully retrieved " + results.length + " scores.");
        callback(null,results)
      },
      error: function(error) {
        console.log("Error: " + error.code + " " + error.message);
        callback(error)
      }
     });
  }

Client code:

  function test()
    {
        var user = fetchUser("example", function(error, user){
         if(error){
          console.error(error)
         }else {
          console.log(user)
         }
      });
 }

Ex 2: Using Promising library

  function fetchUser(username){
    return new Promise(function(resolve, reject){
        var User = Parse.Object.extend("User");
        var query = new Parse.Query("User");
        query.equalTo("username",username);

        query.first({
            success: function(results) {
                console.log("Successfully retrieved " + results.length + " scores.");
                resolve(results)
            },
            error: function(error) {
                console.log("Error: " + error.code + " " + error.message);
                reject(error)
            }
        });
    })
}

Client code:

function test()
    {
      fetchUser("example")
        .then(function(user){
          console.log(user)  
        })
        .catch(function(error){
         console.error(error)
        })  
 }