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POImplementing instance methods/variables in prototypal inheritance
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  1. POImplementing instance methods/variables in prototypal inheritance
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    copied!<p>I've been playing around with prototypal inheritance after reading <a href="http://javascript.crockford.com/prototypal.html" rel="nofollow noreferrer">http://javascript.crockford.com/prototypal.html</a> and having a bit of a problem with understanding how I could make use of it in the way I would use classical inheritance. Namely, all functions and variables inherited by the prototype essentially become statics unless they are overwritten by the child object. Consider this snippet:</p> <pre><code>var Depot = { stockpile : [], loadAmmo : function (ammoType) { this.stockpile.push(ammoType); } }; var MissileDepot = Object.create(Depot); var GunDepot = Object.create(Depot); </code></pre> <p><code>stockpile</code> and <code>loadAmmo</code> definitely should be in the prototype, since both MissileDepot and GunDepot have them. Then we run:</p> <pre><code>MissileDepot.loadAmmo("ICBM"); MissileDepot.loadAmmo("Photon Torpedo"); alert(MissileDepot.stockpile); // outputs "ICBM,Photon Torpedo" alert(GunDepot.stockpile); // outputs "ICBM,Photon Torpedo" </code></pre> <p>This is expected because Neither <code>MissileDepot</code> nor <code>GunDepot</code> actually have <code>stockpile</code> or <code>loadAmmo</code> in their objects, so javascript looks up the inheritance chain to their common ancestor.</p> <p>Of course I could set GunDepot's stockpile manually and as expected, the interpreter no longer needs to look up the chain</p> <pre><code>GunDepot.stockpile = ["Super Nailgun", "Boomstick"]; alert(GunDepot.stockpile); // outputs "Super Nailgun,Boomstick" </code></pre> <p>But this is not what I want. If this were classical inheritance (say Java), loadAmmo would operate on MissileDepot and GunDepot's stockpile independently, as an instance method and an instance variable. <strong>I would like my prototype to declare stuff that's common to children, not shared by them.</strong></p> <p>So perhaps I'm completely misunderstanding the design principles behind prototypal inheritance, but I'm at a loss as how to achieve what I've just described. Any tips? Thanks in advance!</p>
 

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