Get the ASCII value of the character at
$index is negative, it counts from the end of the string.
If the index is outside the bounds of the string, it will return
-1. (Note: It would be simpler if it returned
0, but that is the ASCII code for NULL).
This is the opposite of String.charFromCode.
'a'.getCharCode() //= 97 'abcdef'.getCharCode(3) //= 99 (code for 'c') 'abcdef'.getCharCode(-1) //= 102 (code for 'f') 'abcdef'.getCharCode(100) //= -1