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copied!<p>You can treat functions as objects and give them "member variables". Here we're using an internal function in <code>fact</code>, but instead of just declaring it as a local variable (<code>var loop = ...</code>), we're putting its definition outside of the function, using object syntax (<code>fact.loop = ...</code>). This lets us essentially "export" the internal <code>loop</code> function of <code>fact</code> so that it can be reused by the function <code>doubleFact</code>.</p> <pre><code>var fact = function(n) { return fact.loop(n, 1); }; fact.loop = function(n, acc) { if (n < 1) { return acc; } else { return fact.loop(n-1, acc * n); } }; var doubleFact = function(x) { return fact.loop(x * 2, 1); }; console.log(fact(5)); // 120 console.log(doubleFact(5)); // 3628800 </code></pre> <p>The same idea could be used to maintain state.</p> <pre><code>var countCalled = function() { console.log("I've been called " + (++countCalled.callCount) + " times."); }; countCalled.callCount = 0; countCalled(); // I've been called 1 times. countCalled(); // I've been called 2 times. countCalled(); // I've been called 3 times. </code></pre> <p>If you want to be able to instantiate multiple ones, each with their own state, try this:</p> <pre><code>var CallCounter = function(name) { var f = function() { console.log(name + " has been called " + (++f.callCount) + " times."); }; f.callCount = 0; return f; }; var foo = CallCounter("foo"); var bar = CallCounter("bar"); foo(); foo(); bar(); foo(); bar(); bar(); bar(); console.log(foo.callCount); console.log(bar.callCount); </code></pre> <p>Outputs:</p> <pre><code>foo has been called 1 times. foo has been called 2 times. bar has been called 1 times. foo has been called 3 times. bar has been called 2 times. bar has been called 3 times. bar has been called 4 times. 3 4 </code></pre>

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