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copied!<p>There are only a couple of things that are asynchronous in JavaScript:</p> <ul> <li>Event listeners</li> <li><code>setTimeout</code></li> <li><code>setInterval</code></li> </ul> <p>AJAX uses event listeners internally.</p> <p>So you do someting like:</p> <pre><code>var xhr = new XMLHTTPRequest(); xhr.addEventlistener('readystatechanged', function () { console.log(xhr.responseText); }); </code></pre> <p>If you're working with a callback your code could look something like this:</p> <pre><code>function do_ajax(url, data, callback) { var xhr = new XMLHTTPRequest(); xhr.open("POST", url); xhr.addEventlistener('readystatechanged', function () { if (xhr.readyState==4 && xhr.status==200) { callback(xhr.responseText); } }); } do_ajax("service.php", "foo=bar", function (response) { console.log(response); }); </code></pre> <hr> <p>If you have very complex asynchronous processes I recommend taking a look at <a href="http://wiki.commonjs.org/wiki/Promises/A" rel="nofollow">Promises</a>. <a href="http://api.jquery.com/promise/" rel="nofollow">Here is jQuery's take on promises</a>.</p> <p>You can do something like:</p> <pre><code>when(async_process()).then(function (result) { return do_something_asynchronous(result); // <-- the result is a promise }).done(function (result) { // <-- and the resolved value is the input here console.log(result); }); </code></pre> <p>With Promises your code could look like:</p> <pre><code>headlines.getRandom(true).then(function (random_headlines) { return new HeadLine(random_headlines); }).done(headline) { console.log("And presto!", headline); }); </code></pre>

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