JavaScript array slice edits main array

Asked Jul 29 '17 at 06:32

Active Jul 29 '17 at 06:52

Viewed 26 times

I have the following code, and as of my knowledge Array.slice() is suppose to make a new copy of the main array, but it is not. As you can see, I am editing array "b" and it is modifying the main array "a", which is not what I want.

let a = [ { "a": true }, { "a": true }, { "a": true } ];
let b = a.slice(1, 2);
b[0].b = false;
console.log(a);

It would really help me if someone could give me a hint on how to make a copy from the main array and then edit it without modifying the main array. Thank you

Edit (Solution):

function copy(obj) {
  return Object.assign({}, obj);
}

let a = [ { "a": true }, { "a": true }, { "a": true } ];
let b = a.slice(1, 2).map(copy);
b[0].b = false;
console.log(a);

credit: Ryan

edited Jul 29 '17 at 06:52

asked Jul 29 '17 at 06:32

Shifatul

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It’s not the array; it’s the object itself. `b[0] === a[1]`. If you were to write `b[0] = { a: true, b: false };`, for example – changing the array instead of a value it contains – `a` wouldn’t change. – Ry- Jul 29 '17 at 06:34
@Ryan ohh ok, then what is the proper way to copy an array of objects ? – Shifatul Jul 29 '17 at 06:35
1

To copy one plain object, you can use `Object.assign({}, obj)`, so here `function copy(obj) { return Object.assign({}, obj); } let b = a.slice(1, 2).map(copy);` – Ry- Jul 29 '17 at 06:36
@Ryan it's not working, still same result – Shifatul Jul 29 '17 at 06:41
1

Works fine for me: https://jsfiddle.net/xxnofdkf/ – Ry- Jul 29 '17 at 06:44
@Ryan Look at this - https://jsfiddle.net/j0pay195/ – Shifatul Jul 29 '17 at 06:46
found the err -> missing "{}, obj", thanks so much – Shifatul Jul 29 '17 at 06:48

JavaScript array slice edits main array

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