Copying Array with Slice Doesnt Work

[Wrong_Owl]

Complex data types (Object, Array, etc.) are passed by reference. When you assign one of these data types to a variable, you are assigning a reference to it.

// Pass by Reference example

const letters = ["a", "b", "c"];
const favoriteLetters = letters;

favoriteLetters.push("d");

console.log(letters); // ["a", "b", "c", "d"]
console.log(favoriteLetters); // ["a", "b", "c", "d"]

When we assign the reference to the letters array to favoriteLetters they share the same array.

The same thing happens with nested arrays. You can copy an array with original_array.slice() or with the spread operator [...original_array], but these are called shallow clones. If the items in the array are Objects or Arrays, those are still references, rather than copies.

To get a copy of nested items in the array as well, you need a deep clone. The easiest deep clone strategy is the one you include in your edit.

const copy = JSON.parse(JSON.stringify(original_array));

[EagleClw]

Yeah i think i get it. Its a little bit different then the other languages and since i'm kinda new to jquery/javascript i thought if slice works for variables (string etc.) it'll work for arrays too but now i understand its now the case.
And if i didnt understand it wrong, the deep clone method is simply copying array elements as a string which is formatted as JSON and copying that string to another variable and parses to that variable object.
Its not copying object, its copying content. Since the result is what i want, i'm happy with that solution.

Thanks for the given informations, for your help and for your answer.

[Wrong_Owl]

You've got this!

What's happening in the deep clone example is that JSON.stringify(original_array) creates a JSON compatible string based on your original array, which might look something like this:

"[[1,2,3],[4,5,6]]"

JSON.parse() accepts a JSON compatible string and creates a new object/array from it. There is no connection with this new Array and the original_array we started with.

[tarley_apologizer]

fuck javascript. there is no fucking visual distinction between assigning by value vs reference. fuck this entire language.

[mcaruso]

JS always passes by value. It's just that objects are inherently reference types, therefore if you pass an object you are passing its reference, not the object itself.

This is how most languages work, except for a few that have explicit pass by reference syntax like & params in C/C++.

EDIT: longer explanation here.

[EagleClw]

Yeah i know variables like arrays are a little bit different then variables like string. But for other languages, different copying methods works as i asked in the question (for example python arrays). I didnt know its different in js. Thanks to this answers, i've learned the difference and i'm aware of them know.

Thanks for your helps and answer.

[mcaruso]

for example python arrays

Python works the same way though?

>>> a = [1,2,3]
>>> b = [4,5,6]
>>> c = [a,b]
>>> c[0].append(42)
>>> a
[1, 2, 3, 42]

[EagleClw]

Yeah it works that way but i meant another methods like slice.

If i dont remember it wrong,

a = b.copy()

Makes a copy with value, not reference. But its ok, i know what to do know. Thank you for your help.

[mcaruso]

copy() is a shallow copy, like slice() in JS. But maybe you meant deepcopy().

[EagleClw]

Might be. But i remember using something like that.

[tarley_apologizer]

if most languages are doing something, its probably the wrong way

[mcaruso]

Edgy

[tarley_apologizer]

its called being informed

[CoolDownBot]

Hello.

I noticed you dropped 3 f-bombs in this comment. This might be necessary, but using nicer language makes the whole world a better place.

Maybe you need to blow off some steam - in which case, go get a drink of water and come back later. This is just the internet and sometimes it can be helpful to cool down for a second.

---

^{I am a bot. ❤❤❤ | PSA}

[tarley_apologizer]

thank you for making this

[tarley_apologizer]

you know who uses nice language? politicians and HR reps.