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    <p>Your problem is with this line: <code>$('#some-element').click(this.doSomething);</code></p> <h3>Why this is a problem</h3> <p>JavaScript methods don't know anything about the object that should be assigned to <code>this</code>, it's set when the method is called either explicitly (with <code>myFunction.call(obj)</code>) or implicitly (when called using <code>obj.myFunction()</code>).</p> <p>For example:</p> <pre><code>var x = { logThis: function () { console.log(this); } }; x.logThis(); // logs x x.logThis.call(y); // logs y var func = x.logThis; func(); // logs window: the fallback for when no value is given for `this` </code></pre> <p>In your case, you're passing <code>this.doSomething</code> to jQuery, which is then explicitly calling it with the element that was clicked as the value of <code>this</code>. What's happening is (a slightly more complex version of) this:</p> <pre><code>var callback = this.doSomething; callback.call(anElement, anEvent); </code></pre> <h3>The solution</h3> <p>You need to make sure that <code>doSomething</code> is called with the right value of <code>this</code>. You can do that by wrapping it in another function:</p> <pre><code>var cb = this; $('#some-element').click(function() { return cb.doSomething(); }); </code></pre> <p>jQuery provides a <a href="http://api.jquery.com/jQuery.proxy/" rel="noreferrer"><code>proxy</code></a> function lets you do this more simply:</p> <pre><code>$('#some-element').click(jQuery.proxy(this.doSomething, this)); </code></pre>
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    1. POJavascript callbacks losing 'this'
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    1. USgeorgebrock
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    1. COIn this case `some_box.doSomething();` is already giving me 'undefined' when I call it.. How is that possible? I'm not using any callbacks there
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      1. USAnyone
    2. COThere's a typo in your code: In the constructor function you're setting `this.id` but in the `doSomething` function you're referencing `this.input_id`
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    3. COToo much javascript for 1 day, you're right :(
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