Help with javascript Array mutation

JavaScript
1

Hello! I’m doing the changeMachine project in JS. I want to take “cid” array from the arguments and work with it, but without changing it (I need it later). Then I create two new arrays (originalCid and cidMutable) using cid.slice() method. I thought that after using this method, I would be able to modify the new arrys with no mutation of the original one, but that’s not happening. Can anybody say me why?

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As it can be seen, at line 5 I’m modifying cidMutable, and in the console we can see that cid has been also modified.

Thanks!!

2

don’t use cid.slice() with no params… use spread operator originalCid = […cid] for example.

3

please, don’t post screenshots, copy and paste your code (with proper formatting) or use a repl.it or jsfiddle or codepen or whatever you want

I think the thing is that you have made a copy of the array cid but each array inside the copy is still a reference to those arrays inside cid

I copied a multidimensional array with slice like you did, and this is what happen (the same happen with the spread operator, so @oristar2018 suggestion will still have the same effect) :

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You can try changing approach, or trying to figure it out yourself how to make this work
or this would work if you want the help:

let copy = cid.map(e => [...e]);
4

I tried it and it didn’t work either!

Thanks

5

Thanks! I will post my code next time, I didn’t thought it’s easyer to replicate the problem if all the code is posted!

This comment:
I think the thing is that you have made a copy of the array cid but each array inside the copy is still a reference to those arrays inside cid

Oh my God, it’s really weird… I woult have never thought that the problem was that one… I have found this topic talking about it:

Thanks @ilenia, thank you so much!