I have written a javascript function that uses setInterval to manipulate a string every tenth of a second for a certain number of iterations.

```
function timer() {
var section = document.getElementById('txt').value;
var len = section.length;
var rands = new Array();
for (i=0; i<len; i++) {
rands.push(Math.floor(Math.random()*len));
};
var counter = 0
var interval = setInterval(function() {
var letters = section.split('');
for (j=0; j < len; j++) {
if (counter < rands[j]) {
letters[j] = Math.floor(Math.random()*9);
};
};
document.getElementById('txt').value = letters.join('');
counter++
if (counter > rands.max()) {
clearInterval(interval);
}
}, 100);
};
```

Instead of having the interval set at a specific number, I would like to update it every time it runs, based on a counter. So instead of:

```
var interval = setInterval(function() { ... }, 100);
```

It would be something like:

```
var interval = setInterval(function() { ... }, 10*counter);
```

Unfortunately, that did not work. It seemed like "10*counter" equals 0.

So, how can I adjust the interval every time the anonymous function runs?

Use

`setTimeout()`

instead. The callback would then be responsible for firing the next timeout, at which point you can increase or otherwise manipulate the timing.## EDIT

Here's a generic function you can use to apply a "decelerating" timeout for ANY function call.