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Typically it's a good idea in programming, not just in Javascript but especially in Javascript, to aim

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for pure functions without side effects simply because they are predictable

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and if someone calls them without knowing the function definition, it's always good if you can rely on

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the fact that this function doesn't do anything strange behind the scenes.

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Now that being said, when you're building an application, when you're writing code, it will be impossible

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for you to avoid introducing side effects at some point of time.

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A function might need to set up some event listener or might need to send some data to a server and

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that is absolutely fine.

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The goal just is to minimize the amount of functions which are impure or which have side effects, just

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work with your code in a logical way,

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try to keep your functions predictable and pure

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and if you then occasionally have some functions that need to perform a side effect or that needs to

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be impure, that's absolutely fine.

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Maybe just try to be clear regarding the function naming that this might be a function that does something

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as a side effect,

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for example a function which is named send data to server would be expected to send some data to a

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server and it wouldn't come as a surprise

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that this function as a side effect produces an HTTP request. A function which is just called add

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on the other hand should probably not create some side effect or be impure because a function with this

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name,

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well we would expect this to be pure, right?

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As always, it comes with experience and now of course it's OK to not be perfect regarding that, you should

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definitely be aware of this concept of pure functions though and as I said, aim for more pure functions

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and less impure functions that might introduce side effects.