January 2020
Intermediate to advanced
470 pages
11h 13m
English
Content preview from Mastering JavaScript Functional Programming - Second Edition
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Impure functions
If you decided to completely forego all kinds of side effects, then your programs would only be able to work with hardcoded inputs, and wouldn't be able to show you the calculated results! Similarly, most web pages would be useless: you wouldn't be able to make any web services calls or update the DOM; you'd have static pages only. And your Node code would be really useless for server-side work, as it wouldn't be able to perform any I/O.
Reducing side effects is a good goal in FP, but we shouldn't go overboard with it! So let's think of how to avoid using impure functions, if possible, and how to deal with them if not, looking for the best possible way to contain or limit their scope.
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