How to Sort an Array Without Mutating the Original Array

How can you sort an array without mutating the original array?

You need to copy the array before you sort it. One way with es6:

const sorted = [...arr].sort();

The spread-syntax as array literal (copied from mdn):

var arr = [1, 2, 3];
var arr2 = [...arr]; // like arr.slice()

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Spread_operator

How to sort an array without destroying the original array?

int[] originalArray = {1,5,6,8,4,2};
int[] backup = Arrays.copyOf(originalArray,originalArray.length);
Arrays.sort(backup);

After the execution of the code above, backup becomes sorted and originalArray stays same.

Does .sort function change original array?

Use slice() to sort a copy of the original array.

var arr =[{time:4},{time:3},{time:6}];

arr.sort(function (a, b) {
  return a.time-b.time;
});

will mutate the original array and
returns :

[ { time: 3 }, { time: 4 }, { time: 6 } ]

and console.log(arr) returns

[ { time: 3 }, { time: 4 }, { time: 6 } ]

but

var arr =[{time:4},{time:3},{time:6}];
arr.slice().sort(function (a, b) {
  return a.time-b.time;
});

returns

[ { time: 3 }, { time: 4 }, { time: 6 } ]

but will not affect the original array.

console.log(arr) returns

[ { time: 4 }, { time: 3 }, { time: 6 } ]

How to sort a list without mutating it

If you are using Java 8 or higher, you can use the Stream API. See Sorting a list with stream.sorted() in Java for details.

For example:

List<String> sortedList = myList.stream().sorted().collect(Collectors.toList());

Swap objects in the array without mutating the array

without mutating you mean create a copy? Then like this.

const {activeElementIndex, swapedElementIndex} = action.payload
return {
  ...state,
  stages: (stages => { 
    [stages[activeElementIndex], stages[swapedElementIndex]] =
      [stages[swapedElementIndex], stages[activeElementIndex]];
    return stages })([...state.stages])  
}

(If you want to save an old then just replace [...state.stages] in my code with state.stages)

Reverse array in Javascript without mutating original array

You can use slice() to make a copy then reverse() it

var newarray = array.slice().reverse();

var array = ['a', 'b', 'c', 'd', 'e'];var newarray = array.slice().reverse();
console.log('a', array);console.log('na', newarray);

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