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JavaScript

Posted by Andrey Konovalenko
Andrey Konovalenko
9,409 Points

Need help with array. JavaScript

Hello, people!!! Help me to understand! I want to change order of elements in array. But my code are changing also function argument array (arr) (which is external variable.) instesad of changing only result array.

So I want : [[2,1,3], [1,2,3]]. But return of the function is [[2,1,3],[2,1,3]]. And I don't understand why?

function permutate(arr, index) {
    var result = arr;
    var element = arr[index +1];
    if (arr[index + 1] !== undefined) {
        result[index + 1] = result[index];
        result[index]  =  element;
    } else {
        result[index] = arr[0];
        result[0] = arr[index];
    }
  return [result, arr];
}

permutate([1,2,3], 0);

1 Answer

Steven Parker
Steven Parker
243,656 Points
Steven Parker
Steven Parker
243,656 Points

Array assignment in JavaScript creates a reference to the array.

So anything you do with the new variable affects the original array, and vice-versa.

If you want a copy of the array values instead, you can do that in several ways. But one of the most convenient might be to use a slice method with no arguments:

var newarray = oldarray.slice();
Andrey Konovalenko
Andrey Konovalenko
9,409 Points

Thank you Steven!
I also found the way. 

var newarray = Object.assign([], oldarry);