Short way to replace content of an array

What about this:

// 1. reset the array while keeping its reference
arr1.length = 0;
// 2. fill the first array with items from the second
[].push.apply(arr1, arr2);

See:

1. How to empty an array in JavaScript?
2. .push() multiple objects into JavaScript array returns 'undefined'

You can use splice to replace the content of arr1 with the one of arr2 :

[].splice.apply(arr1, [0, arr1.length].concat(arr2));

This way, all references to arr1 would be correctly updated as this would be the same array with a new content.

As you see, that's possible and easy. But there's normally no reason to do this in a well designed program. If the reason is that you're passing an array to different places, then perhaps you should consider embedding this array in an object.