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copied!<p>The output you've shown doesn't match either of the loops you've shown, but the gist seems to be that you don't want to see the <code>undefined</code> array entries.</p> <blockquote> <p>I understand why it happens, but I want use exactly jQuery $.each for my script.</p> </blockquote> <p>If you really want to do that, it's easy enough:</p> <pre><code>$.each(d, function(i, v){ if (d.hasOwnProperty(i)) { console.log(i); console.log(v); } }); </code></pre> <p>That will weed out the array indexes that don't exist in the array. You <em>could</em> use <code>typeof v[i] !== 'undefined'</code> but that will give you the incorrect result if you've actually set an array element to <code>undefined</code> (so it <em>exists</em>, but its value is <code>undefined</code>).</p> <p>jQuery is iterating over the array in the normal way, starting with index <code>0</code> and going through to index <code>length - 1</code>. The <code>for..in</code> loop loops over the properties in the object, and so doesn't loop for non-existant array entries (but <em>will</em>, the way you've written it, pick up anything from <code>Array.prototype</code> that's enumerable; <a href="http://blog.niftysnippets.org/2010/11/myths-and-realities-of-forin.html" rel="nofollow">more here</a>).</p> <p>Ways to loop things:</p> <ol> <li><p><code>$.each</code>; see above.</p></li> <li><p>Specifically for arrays and array-like things, the staid but useful <code>for (index = 0; index < v.length; ++index)</code>. In this case, because the array is sparse, you'll want <code>v.hasOwnProperty(i)</code> or <code>typeof v[i] !== 'undefined'</code> (if you don't care about the case I listed above) to make sure you're seeing an entry that exists.</p></li> <li><p>For objects in general (including arrays, but you have to be careful): <code>for..in</code>:</p> <pre><code>for (propName in v) { // Check whether `v` has the property itself, or inherited it if (v.hasOwnProperty(propName)) { // `v` has the property itself // If looping an array or array-like thing and you want to see // only the *elements* (properties with numeric indexes) and // skip any non-element properties: if (String(parseInt(propName, 10)) === propName) { // It's an array element } } } </code></pre></li> </ol>

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