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

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);
``````

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, prefereably a way that doesn't require hand-rolling my own sorting algorithm or copying every element of the array into a new one?

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
``````

Another way with es6 (non-deep copy):

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

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

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

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.

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

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

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))
``````

I use Object.assign() for most of my copies:

``````var copyArray = Object.assign([], originalArray).sort();
``````

However, after looking through the OP comments, I researched a bit of deep copying and turns out Object.assign not only performs a shallow copy, but also only selects enumerable and own properties (as answered in this post).

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.