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copied!<p>The line:</p> <pre><code>var bar = new Object( foo ); </code></pre> <p>In your first snippet, it doesn't do anything -you are right with your assumption-, it will simply return a reference to the same object passed to the <code>Object</code> constructor.</p> <p>That's the behavior when you pass a <em>native object</em> to the <code>Object</code> constructor in a <code>new</code> expression (<a href="http://es5.github.com/#x15.2.2.1" rel="nofollow noreferrer"><code>new Object(value)</code></a>), if you pass a <a href="http://webcache.googleusercontent.com/search?q=cache:7jGjZFWhwsgJ:www.jibbering.com/faq/#hostObject" rel="nofollow noreferrer"><em>host object</em></a>, the results are implementation dependent.</p> <p>If you don't pass a value (or you explicitly pass the primitives <code>undefined</code> or <code>null</code>) a new object that inherits from <code>Object.prototype</code> will be created.</p> <p>Otherwise, if you pass any of the remaining primitives (as a Number, String or a Boolean value), a <em>primitive wrapper object</em> will be created (basically "primitive-to-object" type conversion), for example.</p> <pre><code>var s = new String("foo"); // a string object wrapper typeof s; // "object" s.valueOf(); // "foo" </code></pre> <p><sup> See this question about primitives and objects: <a href="https://stackoverflow.com/questions/3907613/how-is-a-javascript-string-not-an-object">How is a Javascript string not an object?</a></sup></p> <p>In your second snippet, the line:</p> <pre><code>var bar = Object.create( foo ); </code></pre> <p>Creates a new object, that inherits from <code>foo</code>, and since it's a different object, when you assign the properties:</p> <pre><code>bar.three = 3; bar.one = 100; </code></pre> <p>Those will be created physically on that separated <em>instance</em>, as you can see, the <code>bar.one</code> property <strong>shadows</strong> the value contained in <code>foo</code>.</p> <p>The object referenced by <code>bar</code>, in fact will contain two <strong>own properties</strong> (<code>one</code> and <code>three</code>, but since it inherits from <code>foo</code>, the property named <code>two</code> is resolvable through the prototype chain, for example:</p> <pre><code>bar.hasOwnProperty('one'); // true, the property is "own" bar.hasOwnProperty('two'); // false, the property is "inherited" from foo bar.two; // 2, is accessible </code></pre> <p>Basically, the prototype chain of <code>bar</code> looks like this:</p> <pre> ----------------- ========> | Object.prototype| ==> null | ----------------- |-------------| [[Prototype]] |---------| | one: 100 | ====================> | one: 1 | (shadowed) | three: 3 | | two: 2 | |-------------| |---------| (== line denotes the prototype chain) </pre>

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