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copied!<p>It <em>is</em> a large problem with Node-based code; you frequently grow "callback pyramids". There are several approaches to dealing with the problem:</p> <p><strong>Code style:</strong></p> <p>Use this annoyance as an opportunity to break your code into bite sized chunks. It means you're likely going to have a proliferation of tiny named funcs - that's probably just fine, though! You might also find more opportunities for reuse.</p> <p><strong>Flow-control Libraries</strong></p> <p>There are exactly 593.72 billion flow control libraries out there. Here's some of the more popular ones:</p> <ul> <li><a href="https://github.com/creationix/step" rel="nofollow">Step</a> super basic serial & parallel flow management.</li> <li><a href="https://github.com/substack/node-seq" rel="nofollow">seq</a> is a heavier but more feature-full flow control library.</li> <li>There's plenty more. Search <a href="http://search.npmjs.org/" rel="nofollow">the npm registry</a> for "flow" and "flow control" (sorry, doesn't appear to be linkable)</li> </ul> <p><strong>Language Extensions</strong></p> <p>There are several attempts to provide a more synchronous-feeling syntax on top of JavaScript (or CoffeeScript), often based on the concepts behind the <a href="http://pdos.csail.mit.edu/~max/docs/tame.pdf" rel="nofollow">tame paper</a>.</p> <ul> <li><a href="http://tamejs.org/" rel="nofollow">TameJS</a> is the OkCupid team's answer to this.</li> <li><a href="http://maxtaco.github.com/coffee-script/" rel="nofollow">IcedCoffeeScript</a> they've also ported TameJS over CoffeeScript as a fork.</li> <li><a href="https://github.com/Sage/streamlinejs" rel="nofollow">streamline.js</a> is very similar to TameJS.</li> <li><a href="http://onilabs.com/stratifiedjs" rel="nofollow">StratifiedJS</a> is a heavier approach to the problem.</li> </ul> <p>This route is a deal-breaker for some:</p> <ul> <li>It's not standard JavaScript; if you are building libraries/frameworks/etc, finding help will be more difficult.</li> <li>Variable scope can behave in unexpected ways, depending on the library.</li> <li>The generated code can be difficult to debug & match to the original source.</li> </ul> <p><strong>The Future:</strong></p> <p>The node core team is very aware of the problem, and are also working on lower level components to help ease the pain. It looks like they'll be introducing <a href="https://groups.google.com/d/msg/nodejs/eVBOYiI_O_A/1ShfZZvb_4QJ" rel="nofollow">a basic version of domains</a> in v0.8, which provide a way of rolling up error handling (avoiding the common <code>return err if err</code> pattern, primarily).</p> <p>This should start to lay a great foundation for cleaner flow control libraries, and start to pave the way for a more consistent way of dealing with callback pyramids. There's too much choice out there right now, and the community isn't close to agreeing on even a handful of standards yet.</p> <p><strong>References:</strong></p> <ul> <li><a href="http://book.mixu.net/ch7.html" rel="nofollow">Mixu's Node book has an awesome chapter</a> on this subject.</li> </ul>

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