You can split on an empty string:
var chars = "overpopulation".split('');
If you just want to access a string in an array-like fashion, you can do that without split
:
var s = "overpopulation";
for (var i = 0; i < s.length; i++) {
console.log(s.charAt(i));
}
You can also access each character with its index using normal array syntax. Note, however, that strings are immutable, which means you can't set the value of a character using this method, and that it isn't supported by IE7 (if that still matters to you).
var s = "overpopulation";
console.log(s[3]); // logs 'r'