Question

What is the minimum refresh time for a js refresh?
What potential problems do I face with super small refreshes like every 40 millisecons… I have a good reason to do so its not madness.

    function refresh(){
    var refreshTime = 40;
    setTimeout("location.reload(true);",refreshTime);
    }

Answer 1

For a single timeout, it doesn’t matter.

Instead of passing a string as a first argument, I recommend to pass a function, which allows more flexibility:

setTimeout(function(){
    //Do anything you want
}, refreshTime);

For intervals (window.setInterval()), I usually take 50 as a minimum, because most tasks do not have to be executed over 20 times a second. Heavy functions in an INTERVAL can cause the browser to freeze (eg: multiple CSS updates -> re-rendering the page).