Redraw Element Within For Loop?

I'm trying to update an element on my page after every iteration of a loop. I'm using a simple innerHTML to achieve this, however, what happens is the page freezes during the entirety of the loop, and finally updates when the loop finishes.

// below function is triggered by clicking some element
function go() {
for (var i = 1; i < len; ++i) {
document.getElementById("output").innerHTML += "Processing #" + i;

[Code]....

Ideally, I'd like the output to update and scroll down as the function processes the data.

Is the problem that innerHTML can't keep up with the speed at which the for loop progresses?