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    <p>This is because <code>50</code> by itself is a Number <em>value</em>, whereas you are returning a Number <em>object</em>.</p> <pre><code>alert(typeof 50); // number alert(typeof (50).abs()); // object </code></pre> <p><a href="http://jsfiddle.net/Pkkaq/" rel="noreferrer">http://jsfiddle.net/Pkkaq/</a></p> <p>Section 4.3.21 of the <a href="http://www.ecma-international.org/publications/files/ECMA-ST/ECMA-262.pdf" rel="noreferrer">ECMAScript reference</a>:</p> <blockquote> <p>A Number object is created by using the Number constructor in a new expression, supplying a Number value as an argument. The resulting object has an internal property whose value is the Number value. A Number object can be coerced to a Number value by calling the Number constructor as a function.</p> </blockquote> <p>In other words, a Number <em>value</em> cannot be strictly equal to a Number <em>object</em>.</p> <pre><code>typeof 50 === typeof new Number(50) //--&gt; false; number != object </code></pre> <p>The reason why <code>(-50).abs()</code> works as expected is because it is being multiplied by <code>-1</code>. When a Number <em>object</em> is multiplied by a Number <em>value</em> it becomes a Number <em>value</em>. In this case, if the parameter is positive, the object is simply returned untouched, causing an <em>object</em> to be returned.</p> <p>Here is a fix for your method, according to the quoted reference above:</p> <pre><code>Number.prototype.abs = function () { return Number(this &gt;= 0 ? this : this * -1); }; </code></pre>
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    1. PO50 === 50: false. 50 == 50: true?
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    1. CO@Jeremy Heiler Maybe you can explain why `typeof (-50).abs()` returns 'number'?
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    2. COBecause when a Number *object* is multiplied by a Number *value* it becomes a Number *value*. If the parameter is already positive, the object is simply returned untouched.
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    3. CO`return this >= 0 ? this * 1 : this * -1;` works just fine. I tried that right after I asked the question, but I figured it's a good chance to give someone a little more reputation, and this actually explains why, which is helpful for the future so I don't fall into this trap again. Congrats, you're a nerd. :)
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