Bracket notation now works on all major browsers, except for IE7 and below.

// Bracket Notation

Test String1[6]



// charAt Implementation

Test String1.charAt(6)

It used to be a bad idea to use brackets, for these reasons (Source):

This notation does not work in IE7.
The first code snippet will return
undefined in IE7. If you happen to use
the bracket notation for strings all
over your code and you want to migrate
to .charAt(pos), this is a real pain:
Brackets are used all over your code
and there's no easy way to detect if
that's for a string or an
array/object.

You can't set the character using this notation. As there is no warning of
any kind, this is really confusing and
frustrating. If you were using the
.charAt(pos) function, you would not
have been tempted to do it.