Add a dash and the number coundt to be from 3 to 5 characters

Hello,

I found a script close to what I need and modified it for my use. However, it comes up with an error at line 13 left? I don't think I have the code quite right. Here is what I have;

// call from format script
// format entry to 99-9 or 99-99 or 99-999 or 99-9999 or 99-99999
function twoDash1() {

//Get the value the user entered, as a string
var s = event.value;

//do nothing if the field is blank
if (!s) return

//allow 3  to 8 characters
if (s.length === 3 || s.length === 4 || s.length === 5 || s.length === 6 || s.length = 7 || s.length === 8) {

// Determine the format string to use
var fs = "99-9" += "-9";
if (s.length === 4) fs;
if (s.length === 5) fs;
if (s.length === 6) fs;
if (s.length === 7) fs;
if (s.length === 8) fs;

//display the formated value
event.value = util.printx(fs, s);

} else {

// let the use know something is wrong
app.alert("Please Enter 3 to 8 characters.", 3);
}

// Call from Keystroke script
// Limit entry to digits only
function DigOnlyKS() {

// Get all that is currently in the field

var val = AFMergeChange(event);

//Reject entry if anything but digits
Event.rc AFExactMatch((/\d*/, val);
}

Any help would be appreciated.

Thank you,

Kelly