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POFunctionscope and Callbacks in Node.js
 

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  1. POFunctionscope and Callbacks in Node.js
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    <p>so i have to calculate some <code>share</code> in a loop. In every iteration of that loop i have to get a variable called <code>rent</code> from an array. So i devided the <code>calculate</code> function from the database stuff.</p> <pre><code>var calculate = function() { while(count &lt; 100) { var share = 50; var shareArray = []; for(var i = 0; i &lt; 100; i++) { var pension = share*2; // mathematical stuff // Gets a rent from a database and returns it in a callback getRent(modules, share, function(rent) { share = rent*foo; // some fancy mathematical stuff going on here // I need to get the share variable above out of its function scope }); // I need the share variable right here shareArray.push(share); // the value of share will be for i = 0: 50, i= 1: 50 ... // This is not what i want, i need the share value from getRent() } count++; } } </code></pre> <p>Now as you may see i am presented with the following trouble. Because I'm working in node.js, the only way to get the <code>rent</code> variable from the modules array is through this callback function called <code>getRent()</code>. The thing is, i need the <code>share</code> value after this step but outside of <code>getRent()</code>. Is there any way i can do this?</p> <p>This is the <code>getRent()</code> - Function:</p> <pre><code>var getRent = function(modules, share, callback) { // Searching for a fitting rent in the modules array // Just assume this is happening here callback(rent); }; </code></pre> <p>So the question is: How can i "return" <code>share</code>:</p> <pre><code>getRent(modules, share, function(rent) { share = rent*foo; // some fancy mathematical stuff going on here // I need to get the share variable above out of its function scope }); </code></pre> <p>in any way?</p>
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    1. COWhat does "getFromDB()" look like? I don't understand how that can work, since fetching from a database almost certainly involves an asynchronous step too.
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    2. COAlso you'd almost certainly be much better off, performance-wise, if you could do **one** query to get all the values you need, rather than a separate query for each one. It's going to be much, much slower to do it one at a time.
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    3. COI'm sorry. This is just a constructed example. The real code would be way to difficult to explain this. Just assume this works. Mhh maybee i'll edit it.
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