barValues is an array I'm passing to a function. Within the function I have this:


var sortedBarValues = barValues;
sortedBarValues.sort(function(a,b){return b - a});


I'm trying to end up with two arrays. barValues being the original array and sortedBarValues being a copy of that array, now sorted.

However, via the two alerts, I'm finding that barValues is ALSO being sorted. Why is that? What is the proper way to make a copy of an array so sort it separately from the original array?

+4  A: 

With the statement var sortedBarValues = barValues;, you are not making a copy of the array. You are only making a reference. Both names refer to the same array.

You can copy it with var sortedBarValues = barValues.slice();. The slice method is meant for slicing arrays, but if you don't pass any parameters to it, it will make a copy.

Keep in mind that using the slice method won't work properly on multi-dimensional arrays. Copying multi-dimensional arrays is somewhat tricky, but jQuery's extend function can do it for you.

You can see information on how to copy an array in this post.

Thanks, Mike. Great explanation.
+1  A: 

When you assigned barValues to sortedBarValues you actually assigned a reference to the original Array. When you sort sortedBarValues, barValues gets sorted as well because they are actually the exact same thing.

You need to make a copy of your array before sorting it, so the other is left unaffected.

var sortedBarValues = Array.apply({}, barValues);
sortedBarValues.sort(function(a, b) { return b - a; });
Alex Barrett
Thanks, Alex. I'm off to look up more info on javascript references!