One large HTML body generating script.
Store the document's URL in str ...
'length' is one of the String object's properties ( and not a method, as in Java ).
Lookup the first slash in the string and return its position, given the first character is number zero.
Store part of the string from its first character, 0 (zero), up to ( not including ) the 'pos' position in 'str2'.
Lookup the last slash...
and store part of the string from its position through the end of the string in str2. So one argument, 'pos' , to the 'substring' method implies the rest of a string from the position indicated.
Since this is a string,...
this results in a string, too, not in a calculated addition.
To distill a number from a string, one function we can use is the 'parseInt' method.
Show the string's third character.
To have a single quote inside a string, escape it with a backslash, ditto for the backslash itself.