NESTED IF/THEN STATEMENT

The answer is that you can create a script that arranges a list of numbers into a list of ranges.  Not exactly an "if" statement, but there will be "if"s 😉

Here's an example:

var aNums = [1,2,3,14,16,17,20];
var aCollect = [];
aNums.forEach(function(a,i,lst){
    // If first or non-consecutive number, then push onto collection
    if(!i || (lst[i-1]!= (a-1))) aCollect .push([a]);
    // If consecutive number,  push onto (keep with)last element in collection
    else aCollect [aCollect .length-1].push(a);
})
// convert to range. 
var aRanges = aCollect .map(function(a){return (a.length == 1)?a[0]:a[0] + "-" + a.pop();})