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

Question

Let\'s suppose I wanted a sort function that returns a sorted copy of the inputted array. I naively tried this

function sort(arr) {
  return arr.sort();
}


        

Answer 1

You can use slice with no arguments to copy an array:

var foo,
    bar;
foo = [3,1,2];
bar = foo.slice().sort();

Answer 2

Just copy the array. There are many ways to do that:

function sort(arr) {
  return arr.concat().sort();
}

// Or:
return Array.prototype.slice.call(arr).sort(); // For array-like objects

Answer 3

Anyone who wants to do a deep copy (e.g. if your array contains objects) can use:

let arrCopy = JSON.parse(JSON.stringify(arr))

Then you can sort arrCopy without changing arr.

arrCopy.sort((obj1, obj2) => obj1.id > obj2.id)

Please note: this can be slow for very large arrays.

Answer 4

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

Answer 5

You can also do this

d = [20, 30, 10]
e = Array.from(d)
e.sort()

This way d will not get mutated.

function sorted(arr) {
  temp = Array.from(arr)
  return temp.sort()
}

//Use it like this
x = [20, 10, 100]
console.log(sorted(x))

Answer 6

Try the following

function sortCopy(arr) { 
  return arr.slice(0).sort();
}

The slice(0) expression creates a copy of the array starting at element 0.