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POIt is said that all Javascript objects have a prototype property, but I only see foo.prototype if foo is a function?
 

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  1. POIt is said that all Javascript objects have a prototype property, but I only see foo.prototype if foo is a function?
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    <p>It is often said that every Javascript object has a <code>prototype</code> property, but I find that <code>foo.prototype</code> has a value only if <code>foo</code> is a function.</p> <p>On Chrome and Firefox, <code>obj.__proto__</code> has a value -- is this the said <code>prototype</code> property? But on IE 9, it won't work (is there some way that can?), and I thought by <code>prototype</code> property, that means <code>obj.prototype</code> should work?</p> <p>I understand that <code>Object.getPrototypeOf(obj)</code> seems to show this <code>prototype</code> property, but why need a special method to get it? Why not just like <code>person.name</code>, which is to get the <code>name</code> property of the <code>person</code> object?</p> <hr> <p><strong>Update:</strong> by the way, <code>obj.constructor.prototype</code> seems to <strong>sometimes</strong> be that prototype, but sometimes not, as in the following code done with Prototypal inheritance with no constructor: (this method is in the Pro Javascript Design Patterns book by Harmes and Diaz by Apress 2008, p. 46)</p> <pre><code>var Person = { name: 'default value', getName: function() { return this.name; } } var reader = clone(Person); console.log(reader.getName()); reader.name = "Ang Lee"; console.log(reader.getName()); function clone(obj) { function F() {}; F.prototype = obj; return new F; } console.log("the prototype of reader is", Object.getPrototypeOf(reader)); console.log(Object.getPrototypeOf(reader) === reader.constructor.prototype); console.log(Object.getPrototypeOf(reader) == reader.constructor.prototype); console.log(Object.getPrototypeOf(reader) === reader.__proto__); console.log(Object.getPrototypeOf(reader) == reader.__proto__); </code></pre> <p>the result will show false, false, true, true for the last 4 lines.</p>
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    1. COObjects are all related to a prototype, but not necessarily by a visible property. In other words, the JavaScript runtime internals know what the prototype object is, but it may not be possible for your code to determine what it is. As to *why* that is true, well, it's just the way that JavaScript was implemented.
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    2. COAnyone who says "every JavaScript object has a prototype property" is referring to the internal property (exposed as `__proto__` on most browsers, as you mentioned).
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    3. COTake a look at this similar question: http://stackoverflow.com/questions/9451881/
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