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    <p>The first two, and the third examples are equivalent, at the end they produce an <code>Array</code> object with only one <em>own property</em>, <code>length</code>, containing <code>5</code> as its value.</p> <p>When you call the <code>Array</code> constructor using a single numeric argument (like <code>Array(5);</code>), the newly created object will contain that number as its <code>length</code> property, the <em>index properties</em> aren't created:</p> <pre><code>var a = Array(5); a.hasOwnProperty('0'); // false </code></pre> <p>The second example produces just the same:</p> <pre><code>var a = []; a.length = 5; a.hasOwnProperty('0'); // false </code></pre> <p>About the third example, it isn't equivalent because it will create a property on the array object, even though its value is <code>undefined</code>:</p> <pre><code>var a = []; a[4] = undefined; a.hasOwnProperty('4'); // true </code></pre> <p>The fourth example:</p> <pre><code>var a = new Array(5); </code></pre> <p>Is just exactly the same as the second one (<code>var a = Array(5);</code>), there's no difference between using the <code>Array</code> constructor with or without the <code>new</code> operator, in the second example you are <a href="http://ecma262-5.com/ELS5_HTML.htm#Section_15.4.1" rel="nofollow">calling the <code>Array</code> constructor as a function</a>.</p> <p>And finally, about your <code>makeArrayToLength</code> function, by now I think you know isn't equivalent at all, since all the "index properties" are initialized to a "default" value. <sub>(BTW don't use <code>default</code> as Identifier, it's a Keyword...)</sub></p> <p>The <code>Array</code> constructor is usually avoided because it can have different behaviors depending the argument used, for example:</p> <pre><code>Array("5"); // one element array, (["5"]) Array(5); // empty array, length = 5 // v.s. ["5"] // one element array [5] // one element array </code></pre> <p>Also, the <code>Array</code> constructor could be overriden, while array literals will always work.</p>
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    1. POIs Array(5) equivalent to var a = []; a.length = 5; in JS?
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    1. POIs Array(5) equivalent to var a = []; a.length = 5; in JS?
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    1. COyou know you could throw me an upvote if you're going to incorporate bits of my answer into yours.
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    2. CO@Hamish, sorry but I didn't "incorporated bits of your answer" in mine, I've just edited to expand my answer (in fact I didn't noticed your answer until I finished editing), and is not the first time [I talk about calling built-in constructors as functions](http://stackoverflow.com/search?q=user:5445+%22constructor+called+as+a+function%22) :), but yes, I think your answer deserves an upvote...
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    3. COSorry if there was a misunderstanding - for some reason I thought you had used the same link, but might have just misread. This answer is very thorough :)
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