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(); } 

and I tested it with this, which shows that my sort method is mutating the array.

var a = [2,3,7,5,3,7,1,3,4]; sort(a); alert(a);  //alerts "1,2,3,3,3,4,5,7,7" 

I also tried this approach

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

but it doesn't work at all.

Is there a straightforward way around this, preferably a way that doesn't require hand-rolling my own sorting algorithm or copying every element of the array into a new one?

Answer 1

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 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