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    <p>The Mozilla implementations just try to emulate exactly the steps that are described in the specification, <code>Object(this);</code> emulates the <em>first step</em>, calling the <a href="http://es5.github.com/#x9.9" rel="noreferrer"><code>ToObject</code></a> internal method:</p> <p>From <code>Array.prototype.forEach</code> <a href="http://es5.github.com/#x15.4.4.18" rel="noreferrer">15.4.4.18</a>:</p> <blockquote> <p>....</p> <p>When the forEach method is called with one or two arguments, the following steps are taken:</p> <ol> <li><p>Let O be the result of calling ToObject passing the this value as the argument.</p></li> <li><p>Let lenValue be the result of calling the [[Get]] internal method of O with the argument "length".</p></li> <li><p>Let len be ToUint32(lenValue).</p></li> </ol> <p>....</p> </blockquote> <p>Calling <a href="http://es5.github.com/#x15.2.1" rel="noreferrer">the Object constructor as a function</a> behind the scenes it performs type conversion, internally as described in <a href="http://es5.github.com/#x15.2.1.1" rel="noreferrer">15.2.1.1</a> the <code>ToObject</code> method is called.</p> <p>There are more things like this if you look carefully, for example, the line:</p> <pre><code>var len = t.length &gt;&gt;&gt; 0; </code></pre> <p>They are emulating a call to the <a href="http://es5.github.com/#x9.6" rel="noreferrer">ToUint32</a> internal method, as described in the step 3, using the unsigned right shift operator (<a href="http://es5.github.com/#x11.7.3" rel="noreferrer"><code>&gt;&gt;&gt;</code></a>). </p> <p><strong>Edit:</strong> The previous lines answer <em>why</em> the Mozilla implementation does it in this way.</p> <p>You might wonder why the ECMAScript spec. needs to call <code>ToObject</code>, check back the <em>Step 2</em>, and it will start to seem obvious:</p> <blockquote> <ol start="2"> <li>Let lenValue be the result of calling the [[Get]] internal method of O with the argument "length".</li> </ol> </blockquote> <p>The spec. needs to ensure that the <code>this</code> value used when the function is called is <em>an object</em>, because primitive values don't have any internal methods, an as you can see on the step 2, the <code>[[Get]](P)</code> internal method is needed, to get the value of the <code>length</code> property.</p> <p>This is done because for <em>strict functions</em> (and also for built-in functions), you can set <em>primitive values</em> as the function's <code>this</code> value, e.g.:</p> <pre><code>(function () {"use strict"; return typeof this; }).call(5); // "number" </code></pre> <p>While for non-strict functions, the <code>this</code> value is always converted to Object:</p> <pre><code>(function () { return typeof this; }).call(5); // "object" </code></pre>
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    1. POWhat's the point of "var t = Object(this)" in the official implementation of forEach?
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    1. POWhat's the point of "var t = Object(this)" in the official implementation of forEach?
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    1. COThanks for the link to the annotated ES5. That'll be very handy!
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    2. COyou're still just answering _what_ rather than _why_ .
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    3. CO@Alnitak, I've answered *why* the *Mozilla implementation* of `forEach` calls the `Object` constructor as a function. But since you want the answer about *why* the *ECMAScript specificacion* uses `ToObject` on the description of the forEach method, I will add it to my answer.
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