Quick Ratios with JavaScript

I always find myself needing to know how numbers compare. But I hate taking out a calculator or grabbing pencil and paper to work it out. So I wrote a small script to do it for me.

Method

Math.Ratio = function (rt1, rt2) {
 var rt1n = rt1.split(':');
 var rt2n = rt2.split(':');

 var rntd1i = false, rntd2i = false;

 for (var i = 0; i < rt1n.length; i++) {
  if (rt1n[i] == '?') {
   rntd1i = i;
  }
 }
 for (var ii = 0; ii < rt2n.length; ii++) {
  if (rt2n[ii] == '?') {
   rntd2i = ii;
  }
 }

 function rtDetermine(r1, r2, ri) {
  var isum = r1[0] / r1[1];
  return ri == 0 ? r2[1] * isum : r2[0] / isum;
 }
 
 if (rntd1i !== false && rntd2i !== false) {
  console.warn('Whoops, can only work with one unknown number.');
  return false;
 } else if (rntd1i !== false) {
  return rtDetermine(rt2n, rt1n, rntd1i);
 } else if (rntd2i !== false) {
  return rtDetermine(rt1n, rt2n, rntd2i);
 } else {
  console.warn('Whoops, need at least one unknown number.');
  return false;
 }
};

And then you can call it like so:

Math.Ratio('1920:1080','?:720');//1280

Demo

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