Splitting Field contents based on line count

I need a solution in place to split a multi line field at a certain point and fill the remaining split text into another field. I have three multi-line fields named Field 1, Field 2, and Field 3. I should say that data is not typed into these fields but rather is populated via a series of functions that grabs data from the other form fields and summarizes results in Field 1. If data does not fit in Field 1 I would like the text to overflow into Field 2..and so on. I already have the code to populate the fields.

I had the idea that the easiest way to do this count the number of paragraph returns and then split when a certain number is reached. I know how to count the returns but not sure how to implement splitting overflow..

So for example, if I have this code:

var count = 0;

var s = getField("Field1").valueAsString;

for (var i = 0; i < s.length; i++) {
    if (s === "\r") count += 1;
}

....and I want to split the text at 50 returns.. then fill Field2.

Can this be done? Maybe there is an easier way than counting returns?

Thanks in advance.