How to repeat a code in html without writing the same code again and again

Have a look at server side includes

Include it like this in your page :

<?php include ('content.html'); ?>

Here is simple JavaScript code to repeat text: (which can be modified as per requirement may be to insert innerHTML)

function repeat(n,Txt){
    for(i=0; i<n;i++)
        document.write(Txt+ char(13)); //char(13) to draw new line
}

Just call this function as per requirement, on window.Load or onclick of a button..

Update: Check this fiddle to Enter repeating HTML fiddle

Code for innerHTML:

function repeat(n,Txt){
    for(i=0; i<n;i++){
        document.getElementById("repeater").innerHTML = 
          document.getElementById("repeater").innerHTML + "<br /> "
           + Txt;
    }
}