simplify logic to remove switch case.

Author: dobon

src/datetime.js

@@ -250,19 +250,18 @@ function toISOTime(
   const desiredPrecision = Precision[normalizeUnit(precision)];
   if (desiredPrecision === undefined) throw new InvalidUnitError(precision);
   const extendedGlyph = extended ? ":" : "";
-  const showSeconds = !suppressSeconds || o.c.millisecond !== 0 || o.c.second !== 0;
-  const showMilliseconds = showSeconds && (!suppressMilliseconds || o.c.millisecond !== 0);
-
-  let c = new String();
-  switch (desiredPrecision) {
-    case Precision.millisecond:
-      c = showMilliseconds ? "." + padStart(o.c.millisecond, 3) : c;
-    case Precision.second:
-      c = showSeconds ? extendedGlyph + padStart(o.c.second) + c : c;
-    case Precision.minute:
-      c = extendedGlyph + padStart(o.c.minute) + c;
-    case Precision.hour:
-      c = padStart(o.c.hour) + c;
+  const showSeconds = !(suppressSeconds && o.c.millisecond == 0 && o.c.second == 0);
+  const showMilliseconds = showSeconds && !(suppressMilliseconds && o.c.millisecond == 0);
+
+  let c = padStart(o.c.hour);
+  if (desiredPrecision >= Precision.minute) {
+    c += extendedGlyph + padStart(o.c.minute);
+  }
+  if (desiredPrecision >= Precision.second && showSeconds) {
+    c += extendedGlyph + padStart(o.c.second);
+  }
+  if (desiredPrecision >= Precision.millisecond && showMilliseconds) {
+    c += "." + padStart(o.c.millisecond, 3);
   }
 
   if (includeOffset) {