Array destructuring via spread operator

Question

The MDN documentation concerning array destructuring is pretty self-explanatory, however, I fail to understand what is happening behind the scenes when destructuring an array like so:

 let Arr = [1, 3, 5, 6]; let newArr = []; [newArr[0], ...newArr] = Arr; console.log(Arr); // returns [1, 3, 5, 6] console.log(newArr); // returns [3, 5, 6] 

How is it that newArr does not inherit the first array member of Arr ?

Answer 1

If you had

[x, ...y] = Arr;

it would be like

x = Arr[0];
y = Arr.slice(1);

so when you have

[newArr[0], ...newArr] = Arr;

it's like

newArr[0] = Arr[0];
newArr = Arr.slice(1);

The assignments involved in destructuring happen left to right. Live:

 const listener = { get foo() { return { set bar(value) { console.log('setting bar'); }, }; }, set foo(value) { console.log('setting foo'); }, }; [listener.foo.bar, ...listener.foo] = [1, 2, 3]; 

Answer 2

It works, but it overwrites with the rest parameters the first value on index zero.

 let array0 = [1, 3, 5, 6], array1 = [], array2 = []; [array2[0], ...array1] = array0; console.log(array0); // [1, 3, 5, 6] console.log(array1); // [3, 5, 6] console.log(array2); // [1] 

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