Better way to detect when a variable != undefined when async request is sent

Given the following:

var doThings = (function ($, window, document) { 
  var someScopedVariable = undefined,
      methods,
      _status;

  methods = { 
    init: function () { 
      _status.getStatus.call(this);

      // Do something with the 'someScopedVariable'
    }
  };

  // Local method
  _status = { 
    getStatus: function () { 
      // Runs a webservice call to populate the 'someScopedVariable'

      if (someScopedVariable === undefined) { 
        _status.setStatus.call(this);
      }

      return someS开发者_如何学运维copedVariable;

    },
    setStatus: function () { 
      $.ajax({
           url: "someWebservice",
           success: function(results){
              someScopedVariable = results;
           }
         });
    }
  };

  return methods;

} (jQuery, window, document));

The issue is clear, this is an async situation were I would like to wait until someScopedVariable is not undefined, then continue.

I thought of using jQuery's .when() -> .done() deferred call but I cant seem to get it to work. I've also thought of doing a loop that would just check to see if its defined yet but that doesnt seem elegant.

Possible option 1:

$.when(_status.getStatus.call(this)).done(function () {
        return someScopedVariable; 
});

Possible option 2 (Terrible option):

_status.getStatus.call(this)

var i = 0;
do {
  i++;
} while (formStatusObject !== undefined);

return formStatusObject;

UPDATE: I believe I stripped out too much of the logic in order to explain it so I added back in some. The goal of this was to create an accessor to this data.

---

I would suggest to wait for the complete / success event of an ajax call.

  methods = { 
    init: function () { 
      _status.getStatus.call(this);
    },
    continueInit: function( data ) {
      // populate 'someScopedVariable' from data and continue init
    }
  };

  _status = { 
    getStatus: function () { 
      $.post('webservice.url', continueInit );
    }
  };

---

You cannot block using an infite loop to wait for the async request to finish since your JavaScript is most likely running in a single thread. The JavaScript engine will wait for your script to finish before it tries to call the async callback that would change the variable you are watching in the loop. Hence, a deadlock occurrs.

The only way to go is using callback functions throughout, as in your second option.

---

I agree with the other answer about using a callback if possible. If for some reason you need to block and wait for a response, don't use the looping approach, that's about the worst possible way to do that. The most straightforward would be use set async:false in your ajax call.

See http://api.jquery.com/jQuery.ajax/

async - Boolean Default: true By default, all requests are sent asynchronously (i.e. this is set to true by default). If you need synchronous requests, set this option to false. Cross-domain requests and dataType: "jsonp" requests do not support synchronous operation. Note that synchronous requests may temporarily lock the browser, disabling any actions while the request is active.