first commit

script.js

@@ -0,0 +1,65 @@
+const form = document.getElementById('convert');
+
+const values = {
+  'Quadrans': 1,
+  'Semis': 2,
+  'As': 4,
+  'Dupondius': 8,
+  'Sestertius': 16,
+  'Quinarius argenteus': 32,
+  'Denarius': 64,
+  'Quinarius aureus': 800,
+  'Aureus': 1600,
+}
+
+function gcd(a,b) {
+  if(a==0) {
+    return 1;
+  }
+  console.log(a,b);
+  if(a<b) {
+    return gcd(b,a);
+  }
+  while(b) {
+    const [m,c] = [a%b,b];
+    a = c;
+    b = m;
+  }
+  return a;
+}
+
+function update() {
+  const fd = new FormData(form);
+  const {num_from, from, to} = Object.fromEntries(Array.from(fd));
+  console.log(num_from,from,to);
+
+  const value_from = values[from];
+  const value_to = values[to];
+  let [n,d] = value_to > value_from ? [num_from, value_to/value_from] : [num_from * value_from/value_to, 1];
+  const g = gcd(n,d);
+  n /= g;
+  d /= g;
+  const output = d==1 ? n : `${n} / ${d}`;
+  document.querySelector('output').textContent = output;
+}
+
+function swap() {
+  const fd = new FormData(form);
+  const {num_from, from, to} = Object.fromEntries(Array.from(fd));
+
+  const value_from = values[from];
+  const value_to = values[to];
+
+  document.getElementById('num_from').value = num_from * value_from/value_to;
+  
+  document.getElementById('from').value = to;
+  document.getElementById('to').value = from;
+
+  update();
+}
+
+update();
+
+form.addEventListener('input', update);
+
+document.getElementById('swap').addEventListener('click', swap);