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April 12, 2017 09:22
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Demonstration of how to RELEASE ZALGO
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/** | |
* Demonstration of how to RELEASE ZALGO | |
* @author Bastian Masanek (2017) | |
*/ | |
let cache; | |
function releaseZalgo(cb) { | |
if (cache) { | |
// This is synchronous and execucted immediately. | |
// YOU JUST RELEASED ZALGO! | |
return cb(cache); | |
// Correct approach: | |
// return process.nextTick(() => cb(cache)); | |
} | |
// Any async operation here. | |
setTimeout(() => { | |
cache = 'All fine.'; | |
cb(cache); | |
}, 1000); | |
} | |
function zalgoFactory() { | |
let listeners = []; | |
releaseZalgo(data => { | |
listeners.forEach(listener => listener(data)); | |
}); | |
return { | |
onData: listener => listeners.push(listener) | |
}; | |
} | |
let a = zalgoFactory(); | |
a.onData(data => { | |
console.log('data from a:', data); | |
let b = zalgoFactory(); | |
// This will never be called because releaseZalgo() already executed | |
// BEFORE .onData() was even defined. | |
b.onData(data => { | |
console.log('data from b:', data); | |
}); | |
let c = zalgoFactory(); | |
// This will never be called because releaseZalgo() already executed | |
// BEFORE .onData() was even defined. | |
c.onData(data => { | |
console.log('data from c:', data); | |
}); | |
}); | |
/* | |
Example output: | |
$ node zalgo.js | |
data from a: All fine | |
Nothing else will happen after the first asynchronous call. | |
=============================================================================== | |
RULE OF THUMB: | |
------------------------------------------------------------------------------- | |
Use Promises. You can't release Zalgo when using Promises: | |
function releaseZalgo() { | |
if (cache) { | |
return Promise.resolve(cache); | |
} | |
return new Promise((resolve, reject) => { | |
... | |
}); | |
} | |
If you have (or want) to use callbacks, choose whether your function is | |
synchronous or asynchronous -- and stick with it. | |
Never mix those concepts, because it can lead to unpredictable, weird and | |
thus hard to track down errors in your application. | |
If you find Zalgo, you can fight it using process.nextTick(). | |
References: | |
- Designing APIs for Asynchrony | |
http://blog.izs.me/post/59142742143/designing-apis-for-asynchrony | |
- Don't release Zalgo! | |
https://github.com/oren/oren.github.io/blob/master/posts/zalgo.md | |
=============================================================================== | |
*/ |
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