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    <p>First of all, do not forget the <code>var</code> keyword when declaring variables. When you declare <code>value = 42</code> inside <code>myFunc</code>, you are actually creating a variable in the global namespace instead of the function scope. It should start like this:</p> <pre><code>function myFunc() { var value = 42; </code></pre> <p>Now, <code>myObject.result</code> is returning 42 because <code>myFunc</code> returns your <code>result</code> object which contains a copy of the <code>value</code> variable declared inside the function.</p> <p>Your functions <code>setValue</code>, <code>getValue</code> and <code>incrementValue</code> are changing the value of <code>value</code>, not <code>result.value</code>. When you call <code>myObject.value</code>, you are getting the value from the returned object, not the inner variable of your function.</p> <p>You could get it to work using something like this:</p> <pre><code>function myFunc() { var value = 42; var result = { value: value, getValue: getValue, incrementValue: incrementValue, setValue: setValue }; return result; function setValue(y) { result.value = y; } function getValue() { return result.value; } function incrementValue() { result.value++; } } </code></pre> <p>However, there are better design patterns than this. You could use the <code>new</code> keyword and <code>prototype</code> to define the methods available for the objects returned from your function. Take this example:</p> <pre><code>function myFunc() { this.value = 42; } myFunc.prototype.setValue = function(y) { this.value = y; } myFunc.prototype.getValue = function(y) { return this.value; } myFunc.prototype.incrementValue = function(y) { this.value++; } var myObject = new myFunc(); console.log(myObject.getValue()); // 42 myObject.setValue(30); myObject.incrementValue(); console.log(myObject.getValue()); // 31 </code></pre>
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    1. USGuilherme Sehn
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    1. COIt would be nice if you explain that primitives are copied. That is why value is copied to the return object. On the other hand, objects are not copied. For them, assignments are just an alias for the same obect.
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      1. USWalter Macambira
    2. CO@Walter: This might actually be an implementation detail. Since primitive values are *immutable* you cannot tell (by executing the code only) whether primitives are also not just references.
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      1. USFelix Kling
    3. CONote that both examples expose a different behavior than the OP's code. In both of them you can also change the value through `myObject.value = newValue;` (in addition to `myObject.setValue`). This wasn't possible in the original code.
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