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POIn node.js programming, how do you handle the scenario where a callback doesn't fire?
 

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  1. POIn node.js programming, how do you handle the scenario where a callback doesn't fire?
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    <p>A frequently used asynchronous function call idiom in node.js is to use callback functions like this:</p> <pre><code>library.doSomething(params, function(err,result) { if (err) { ... handle error, retry etc } else { ... process results, be happy! } }); </code></pre> <p>It's great - you call something, then later on handle the results or an error. There is unfortunately an excluded third option... that the code you've called never executes your callback. What are the best approaches to handle the possibility of a callback never getting called?</p> <p>A lot of the time, especially if you're writing a library that relies on the network, you need to guarantee that you will call any callbacks passed to you once and only once. With that in mind, a pattern something like this looks like the way to go:</p> <pre><code>// set a timout var failed = false, callbackFailure = setTimeout(function() { ... handle failure, call further pending callbacks with a timeout error failed = true; },30000); library.doSomething(params, function(err,result) { if (!failed) { clearTimeout(callbackFailure); if (err) { ... handle error, retry etc } else { ... process results, be happy again! } } }); </code></pre> <p>It seems like a matter of faith that any callback you expect to fire actually will fire, and I'm sure all programmers have run into scenarios where callbacks simply won't execute for whatever reason - cosmic rays, sunspots, network failures, bugs in a third party library, or ... <em>gasp</em> ... bugs in your own code.</p> <p>Is something like my code example actually a good practice to adopt or has the node.js community already found a better way to handle it?</p>
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      1. POIn node.js programming, how do you handle the scenario where a callback doesn't fire?
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    1. COEh, this is a silly question ( and not constructive ). It's like asking: can you guarantee that any code in any language works as it should? The answer is: you can't! Good administrator will monitor his application all the time. After all everything can fail due to "cosmic rays". This has **nothing** to do with Node.js. The engine is fine. It is tested heavily all the time.
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      1. POIn node.js programming, how do you handle the scenario where a callback doesn't fire?
      1. USfreakish
    2. COCouldn't you just defensively use try{...}catch{...} blocks?
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      1. USLouis Ricci
    3. CO@freakish - node js has some shortcomings with regards to async error handling, this link seems pretty interesting. http://stella.laurenzo.org/2011/03/bulletproof-node-js-coding/
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