Question

Suppose you have a webpage that keeps refreshing, like so – how can you display a text-counter that counts to 10 ?

Answer 1

Simple javascript would work.

use the function setinterval() to run some code (you can chose the time interval in miliseconds).

An example of this is here:

http://www.w3schools.com/jsref/met_win_setinterval.asp

Combine this with the getElementById function

document.getElementById('my_div').innerHTML = a_variable;

and a div like so

<div id="my_div"></div>

(or instead of the div update a text input box like on the w3 example)
I’ve refrained from writing the code for you, but writing it should be good practice and more valuable for you.

P.S. Iam & Dave answered the question which was posed in your title – the title is slightly inaccurate. Better would be “In JavaScript how would you change the inner html of the body of a webpage at regular intervals”