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    <p>Your problem here is not <em>exactly</em> a closure or scoping problem. The problem is that when you assign <code>this.readSuccess</code> to a variable, you assign the function itself without any notion of the object it originaly belongs to.</p> <p>In the same way, you can take a regular, "stand-alone" function and use it as method of an object:</p> <pre><code>function hello() { alert("Hello "+this.planet); } var planet = "Earth"; hello(); // -&gt; 'Hello Earth' var Venus = { planet: "Venus" }; hello.apply(Venus); // -&gt; 'Hello Venus' Venus.hello = hello; Venus.hello(); // -&gt; 'Hello Venus' </code></pre> <p>And your problem can be replicated in this example</p> <pre><code>var helloVenus = Venus.hello; helloVenus(); // -&gt; 'Hello Earth' </code></pre> <p>So your problem is to assign this.readSuccess to some variable <strong><em>and having it called as a method of this</em></strong>. Which can be done with a closure as demonstrated by Pointy. Since I don't know what "SomeAjaxCall" actually does, it's hard to know if the value of <code>this</code> is actually lost and if <code>var obj = this</code> is actually needed. Chances are that it's not, so you can be fine with this kind of code:</p> <pre><code>var helloVenus = function() { Venus.hello() } helloVenus(); // -&gt; 'Hello Venus' </code></pre> <p>In your case, that would be (<strong>edit:</strong> adding the arguments passed to the handler) :</p> <pre><code>SomeObject.prototype.refreshData = function() { var read_obj = new SomeAjaxCall( "read_some_data", { }, function () { this.readSuccess.apply(this, arguments) }, function () { this.readFail.apply(this, arguments) } ); } </code></pre> <p>As noted previously, several js frameworks offer a <code>bind</code> function to simplify this kind of issue. But you don't need a complete framework just for this : here is a perfectly fine <code>Function#bind</code> method that works an plain javascript:</p> <pre><code>Function.prototype.bind = function(obj) { var __method = this; var args = []; for(var i=1; i&lt;arguments.length; i++) args.push(arguments[i]); return function() { var args2 = []; for(var i=0; i&lt;arguments.length; i++) args2.push(arguments[i]); return __method.apply(obj, args.concat(args2)); }; } </code></pre> <p>With the help of <code>Function#bind</code>, you can write:</p> <pre><code>SomeObject.prototype.refreshData = function() { var read_obj = new SomeAjaxCall( "read_some_data", { }, this.readSuccess.bind(this), this.readFail.bind(this) ); } </code></pre>
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    1. POScoping problem with Javascript callback
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    1. COThis is a great answer. Thanks a lot for the info.
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    2. COand bind is part of ECMAScript 5 now: https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/Function/bind
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