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POHow to access an object from a callback function?
 

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  1. POHow to access an object from a callback function?
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    <p>I feel bad because it is very likely this has already been answered and I am just not using the right search terms. I am very new to asynchronous JavaScript. So, I will lead with an apology. If someone could even just help me get the right search terms I would most appreciate it.</p> <p>I am trying to use the Google feeds api. I have it working when I follow the stock example as laid out in the hello world section. I am trying to make something that is a little more extensible so that I can use it in several places. So I created an object...</p> <pre><code>function AlertRSS(num, url, div, date) { this.num = typeof num !== 'undefined' ? num : 5; this.url = typeof url !== 'undefined' ? url : 'http://arstechnica.com/author/caseyjohnston/feed/'; this.sel = typeof sel !== 'undefined' ? sel : '#alert'; this.date = typeof date !== 'undefined' ? date : this.getYesterday(); } </code></pre> <p>I then try to call the object inside of the method...</p> <pre><code>AlertRSS.prototype.displayFeed = function() { var retval = null; var feed = new google.feeds.Feed(this.url); feed.load(function(result) { var tmp = this; if (!result.error) { for ( var i = 0; i &lt; result.feed.entries.length; i++) { var entry = result.feed.entries[i]; console.log(sel + ' &lt;h2&gt;&lt;a href="' + entry.link + '"&gt;' + entry.title + '&lt;/a&gt;&lt;/h2&gt;&lt;br /&gt;'); $(tmp.sel).append('&lt;h2&gt;&lt;a href="' + entry.link + '"&gt;' + entry.title + '&lt;/a&gt;&lt;/h2&gt;&lt;br /&gt;'); } } }); }; </code></pre> <p>However, it seems like I am not able to access the properties from the object. I keep getting a <code>Uncaught ReferenceError: sel is not defined</code> in the console. </p> <p>I think the issue is related to scope, but at this point I feel a little out of my depth. Any help would be most appreciated.</p> <h1>Update</h1> <p>For a first post this was a travesty. I had numerous mistakes in my code. Both responses were correct. However, in case another poor newb like me sees this question, I wanted to put working code out there. </p> <p>The issue turned out to be placement of the <code>var tmp = this;</code> line. It needs to be placed outside of the internal callback function to work. As per Tomasz Nurkiewicz suggestion, I also changed <code>var tmp</code> to <code>var that</code>. Working code is as follows:</p> <pre><code>function AlertRSS(num, url, sel, date) { this.num = typeof num !== 'undefined' ? num : 5; this.url = typeof url !== 'undefined' ? url : 'http://arstechnica.com/author/caseyjohnston/feed/'; this.sel = typeof sel !== 'undefined' ? sel : '#alert'; this.date = typeof date !== 'undefined' ? date : this.getYesterday(); } AlertRSS.prototype.displayFeed = function() { var feed = new google.feeds.Feed(this.url); var that = this; feed.load(function(result) { if (!result.error) { for ( var i = 0; i &lt; result.feed.entries.length; i++) { var entry = result.feed.entries[i]; console.log(that.sel + ' &lt;h2&gt;&lt;a href="' + entry.link + '"&gt;' + entry.title + '&lt;/a&gt;&lt;/h2&gt;&lt;br /&gt;'); $(that.sel).append('&lt;h2&gt;&lt;a href="' + entry.link + '"&gt;' + entry.title + '&lt;/a&gt;&lt;/h2&gt;&lt;br /&gt;'); } } }); }; </code></pre>
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