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    <p>One should avoid the pyramid of doom:</p> <pre class="lang-js prettyprint-override"><code>var express = require('express'); var Q = require('Q'); var app = express(); app.get('/',function(req,res){ var mysql = require('mysql'); var connection = mysql.createConnection({ host : 'localhost', user : 'root', password : '' }); connection.connect(); function doQuery1(){ var defered = Q.defer(); connection.query('SELECT 1 AS solution',defered.makeNodeResolver()); return defered.promise; } function doQuery2(){ var defered = Q.defer(); connection.query('SELECT 2 AS solution',defered.makeNodeResolver()); return defered.promise; } Q.all([doQuery1(),doQuery2()]).then(function(results){ res.send(JSON.stringify(results[0][0][0].solution+results[1][0][0].solution)); // Hint : your third query would go here }); connection.end(); }); app.listen(80); console.log('Listening on port 80'); </code></pre> <p>This sample show a result which depend of 2 independent computed values. Each of these values a queried in doQuery1 and doQuery2. They are executed in sequence, but asynchronously.</p> <p>Next you can see <code>Q.all(...</code> which basically call the "then" callback on success. Within that callback, the calculation is done.</p> <p>Using promises (details : <a href="https://github.com/kriskowal/q/blob/master/README.md" rel="noreferrer">Github Q: promise for Javascript</a> and <a href="http://en.wikipedia.org/wiki/Promise_(programming)" rel="noreferrer">wikipedia</a> ) permit to make your code cleaner, separate computation and handling of results and move things arround.</p> <p>Look at how easy it would be to add "doQuery3" as prerequisit for your calculation !</p> <p>And bellow the "package.json" bellonging to the sample code:</p> <pre class="lang-js prettyprint-override"><code>{ "name": "hello-world", "description": "hello world test app", "version": "0.0.1", "private": true, "dependencies": { "express": "3.2.0", "q": "0.9.3", "mysql":"2.0.0-alpha7" } } </code></pre>
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