SetTimeout Problem Nested In A For Loop

I've encountered a problem with setTimeout() which I haven't really been able to solve. The problem is that setTimeout works like this:

setTimeout(code, delay) {

// In delay milliseconds, evaluate code

}

Here's the setTimeout I'm trying to use:

setTimeout("result_area.innerHTML += result_string;", delay);

This is nested in a for loop, where result_string changes every time. This raises a problem because what it tries to do is this:

// In delay milliseconds, evaluate "result_area.innerHTML += result_string;"

What I want it to do is the following:

// In delay milliseconds, add whatever result_string is right now to result_area.innerHTML

Unfortunately I can't figure out a way to do this. Does anyone have any answers for me?