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POjQuery.when understanding
 

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    <p>I am trying to use the <code>jQuery.when</code> to fire two <code>ajax</code> requests and then call some function after the two requests have completed. Here's my code:</p> <pre><code>var count = 0; var dfr; var showData = function(data) { dfr.resolve(); alert(count); // Do something with my data data received }; var method1 = function() { dfr = $.Deferred(); return $.ajax('localhost/MyDataService/DataMethod_ReturnsData', { dataType: "jsonp", jsonp: "$callback", success: showData }); }; var method2 = function() { return $.ajax('localhost/MyDataService/DataMethod_ReturnsCount', { dataType: "jsonp", jsonp: "$callback", success: function(data) { count = data.d.__count; } }); }; $.when(method1(), method2()) .then(showData()); </code></pre> <p>However this is not working as expected. Ajax call in <code>method1</code> will return data which is to be used in <code>showData()</code> and Ajax call in <code>method2</code> will return count which is to be assigned to var count and later used in <code>showData()</code>. </p> <p>But when I fire the above code, <code>method1</code> gets called and then <code>method2</code> and then <code>showData</code> leaving the data in <code>showData</code> as <code>'undefined'</code>. How can I achieve this via <code>$.when</code> which as far as I know proceeds only when both functions returning <code>$.promise</code> are executed. I want that both the ajax calls should be called in parallel and later results be displayed based on results from both calls.</p>
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    1. COYou don't need the `dfr = $.Deferred()` at all, because the [`jqXhr`](http://api.jquery.com/Types/#jqXHR) returned by `$.ajax()` is a deferred. Not sure if that will fix the problem here, but it's definitely unnecessary. The problem might be that you're using `.then()` instead of `.done()`.
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    2. COI was referring to the post by eric hynds [http://www.erichynds.com/jquery/using-deferreds-in-jquery/] where he too used the $.when and then callbacks.
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    3. COyou only need that if you're using an object which doesn't handle deferred's directly. Eric's demo uses a timer object, so he has to manaully "resolve" a deferred object that he created himself when the timer expires. Like Matt says, if it's an AJAX query you don't need it.
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