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POHow to avoid global variables in JavaScript?
 

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  1. POHow to avoid global variables in JavaScript?
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    <p>We all know that <a href="http://en.wikipedia.org/wiki/Global_variable" rel="noreferrer">global variables</a> are anything but best practice. But there are several instances when it is difficult to code without them. What techniques do you use to avoid the use of global variables?</p> <p>For example, given the following scenario, how would you not use a global variable?</p> <p><strong>JavaScript code:</strong></p> <pre><code>var uploadCount = 0; window.onload = function() { var frm = document.forms[0]; frm.target = "postMe"; frm.onsubmit = function() { startUpload(); return false; } } function startUpload() { var fil = document.getElementById("FileUpload" + uploadCount); if (!fil || fil.value.length == 0) { alert("Finished!"); document.forms[0].reset(); return; } disableAllFileInputs(); fil.disabled = false; alert("Uploading file " + uploadCount); document.forms[0].submit(); } </code></pre> <p><strong>Relevant markup:</strong></p> <pre><code>&lt;iframe src="test.htm" name="postHere" id="postHere" onload="uploadCount++; if(uploadCount &gt; 1) startUpload();"&gt;&lt;/iframe&gt; &lt;!-- MUST use inline JavaScript here for onload event to fire after each form submission. --&gt; </code></pre> <p>This code comes from a web form with multiple <code>&lt;input type="file"&gt;</code>. It uploads the files one at a time to prevent huge requests. It does this by <a href="http://en.wikipedia.org/wiki/POST_%28HTTP%29" rel="noreferrer">POST</a>ing to the iframe, waiting for the response which fires the iframe onload, and then triggers the next submission.</p> <p>You don't have to answer this example specifically, I am just providing it for reference to a situation in which I am unable to think of a way to avoid global variables.</p>
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