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how functional is being able to do a copy of some types of variables with `=` and some not?

Array.map is supposed to take an array and return a new one, with the elements transformed by the function in the callback

Why do you think I'm using map strangely?

your doesn't actually do any transforming

it just makes an array full of ["12345"] and undefined

The {"12345] is uniquely in there because the return value of an assignment is the value assigned

That's why I asked about side effects in your map function

Your code is confusing because it uses map just to iterate over an array and set a value.  forEach is more what you want

Map is widely use to modify the same array is iterating over in this case my Map is only modifying two matching properties...

&gt;Since map builds a new array, using it when you aren't using the returned array is an anti-pattern; use forEach or for-of instead. Signs you shouldn't be using map: A) You're not using the array it returns, and/or B) You're not returning a value from the callback.

<https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/map#Description>

```oSearch.filters = 
oSearch.filters.map.......```

it would have set the filters, but it would have been the wrong filters because your map function returns weird stuff

```
var filters = oSearch.filters;
filters.map ....
oSearch.filters = filters
```

i think that might have actually worked, but its an abomination

<@U5TF1GQ20> Let me present to you the abomination...

one is modifying an existing array, the other is creating a new one

the elements of arr will be doubled after the forEach example, the elements of arr will not be doubled in the map example

Yeah you can't compare those because they have different effects.  See the link I posted

&gt;Since map builds a new array, using it when you aren't using the returned array is an anti-pattern; use forEach or for-of instead. Signs you shouldn't be using map: A) You're not using the array it returns, and/or B) You're not returning a value from the callback.

<https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/map#Description>

<@U5TF1GQ20> I can recreate the example to do the same but I don't really have time for that... I think we have different perceptions, that is all... peace... :v:

<@U8CT0V220> This is very valid point I will consider for sure...
Since map builds a new array, using it when you aren't using the returned array is an anti-pattern; use forEach or for-of instead. Signs you shouldn't be using map: A) You're not using the array it returns, and/or B) You're not returning a value from the callback.