How to handle common code in multiple HTML's using javascript or jQuery

Question

I have an application which has almost 30 html\'s and they share some common code to which i f i made any changes i need to change it on every page. Below is the piece of code w

Answer 1

You already got answer for PHP, but if you don't want or can't use it you can save it in JS file: test.js

document.write('
\n\
  
\n\
    
\n\
    
\n\
    
\n\
    
\n\
  
\n\
 
');

and include it:

But of course better with PHP.