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POHow to structure javascript callback so that function scope is maintained properly
 

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    <p>I'm using XMLHttpRequest, and I want to access a local variable in the success callback function.</p> <p>Here is the code:</p> <pre><code>function getFileContents(filePath, callbackFn) { var xhr = new XMLHttpRequest(); xhr.onreadystatechange = function() { if (xhr.readyState == 4) { callbackFn(xhr.responseText); } } xhr.open("GET", chrome.extension.getURL(filePath), true); xhr.send(); } </code></pre> <p>And I want to call it like this:</p> <pre><code>var test = "lol"; getFileContents("hello.js", function(data) { alert(test); }); </code></pre> <p>Here, <code>test</code> would be out of the scope of the callback function, since only the enclosing function's variables are accessible inside the callback function. What is the best way to pass <code>test</code> to the callback function so the <code>alert(test);</code> will display <code>test</code> correctly?</p> <p>Edit: </p> <p>Now, if I have the following code calling the function defined above:</p> <pre><code>for (var test in testers) { getFileContents("hello.js", function(data) { alert(test); }); } </code></pre> <p>The <code>alert(test);</code> code only prints the last value of <code>test</code> from the <code>for</code> loop. How do I make it so that it prints the value of <code>test</code> during the time at which the function <code>getFileContents</code> was called? (I would like to do this without changing <code>getFileContents</code> because it's a very general helper function and I don't want to make it specific by passing a specific variable like <code>test</code> to it.</p>
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    1. COSee also: http://stackoverflow.com/questions/tagged/javascript+closures+loops
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