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POBased on how they are constructed, can callbacks also be defined as closures?
 

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    <p>In JavaScript, I know that a closure is can be defined as a nested function that has access to its containing function's variables. For example:</p> <pre><code>function outerFunction(x, y) { function innerFunction() { return x + y + 10; } return innerFunction; } </code></pre> <p>Now, the following code is wiring up a callback for the <code>onreadystatechange</code> property of the request object; however, <strong>I was wondering if, by definition, this is also considered to be a closure</strong>:</p> <pre><code>/* This is a contrived example, I know. * Bear with me - it demonstrates the point I'm trying to convey. */ function submitHandler() { var oRequest = createRequest(); // assume I'm getting an instance of the xhr var sUsername = 'Tom'; // assume this is needed for work in the handler var This = this; oRequest.onreadystatechange = function() { This.handleResponse(oRequest, sUsername) } } function handleResponse(oResponse, sUsername) { if(oResponse.readyState === 4 &amp;&amp; oResponse.status === 200) { // do work with the username } else { // we're not done yet... } } </code></pre> <p>I realize that the <code>handleResponse</code> function could also just be written as an anonymous function in the context of <code>submitHandler</code>, but I find that more complex Ajax code can be more readable and easily maintained if callbacks are defined outside the scope of the function calling back to them. Again, this is a contrived example that I'm using in hopes of simply demonstrating the point of my question.</p>
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