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POHow do I find "prototype" values in javascript?
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  1. POHow do I find "prototype" values in javascript?
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    copied!<p>I use the following function to detect values that belonged to an object's <em>constructor</em> instead of the object itself.</p> <pre><code>function isAPrototypeValue(object, key ) { return !(object.constructor &amp;&amp; object.constructor.prototype[key]); } </code></pre> <p>this would work as follows:</p> <pre><code>Array.prototype.base_value = 'base' var array = new Array; array.custom_value = 'custom' alert( isAPrototypeValue( array, 'base_value' ) ) // true alert( isAPrototypeValue( array, 'custom_value' ) ) // false </code></pre> <p><strong><em>But</em></strong> when I started to use inheritance:</p> <pre><code>function Base() { return this }; Base.prototype.base_value = 'base'; function FirstSub() { return this }; FirstSub.prototype = new Base(); FirstSub.prototype.first_value = 'first'; function SubB () { return this }; SecondSub.prototype = new FirstSub(); SecondSub.prototype.second_value = 'second'; result = new SecondSub(); </code></pre> <p>and I called</p> <pre><code>alert( result.constructor ) </code></pre> <p>I would get <strong>Base</strong> instead of the expected <strong>SecondSub</strong>, which itself is not a big problem, But...</p> <p>if I extended <strong>result</strong> like this:</p> <pre><code>result.custom_value = 'custom' result.another_value = 'another' </code></pre> <p>I would have expected to be able to distinguish between values that belong to <strong>result</strong> or values that belong to <strong>SecondSub, FirstSub and Base</strong>;</p> <p>eg.</p> <pre><code>alert( isAPrototypeValue( result, 'custom_value' ) ) // false ( as expected ) alert( isAPrototypeValue( result, 'base_value' ) ) // true ( as expected ) alert( isAPrototypeValue( result, 'first_value' ) ) // true extend, but it is false alert( isAPrototypeValue( result, 'second_value' ) ) // true extend, but it is false </code></pre> <p>How can I change <strong>isAPrototypeValue</strong> to churn out the expected results?</p>
 

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