Terse way to intersperse element between all elements in JavaScript array?

Question

Say I have an array var arr = [1, 2, 3], and I want to separate each element by an element eg. var sep = \"&\", so the output is [1, \"&a

Answer 1

javascript has a method join() and split()

var arr = ['a','b','c','d'];
arr = arr.join('&');
document.writeln(arr);

Output should be: a&b&c&d

now split again:

arr = arr.split("");

arr is now:

arr = ['a','&','b','&','c','&','d'];