adopt isoformat for dates

package.json

@@ -39,5 +39,8 @@
     "rollup": "^2.37.1",
     "rollup-plugin-node-resolve": "^5.2.0",
     "rollup-plugin-terser": "^7.0.2"
+  },
+  "dependencies": {
+    "isoformat": "^0.2.0"
   }
 }

src/formatDate.js

@@ -1,29 +1,5 @@
-function pad(value, width) {
-  var s = value + "", length = s.length;
-  return length < width ? new Array(width - length + 1).join(0) + s : s;
-}
-
-function isUTCMidnight(date) {
-  return date.getUTCMilliseconds() === 0
-      && date.getUTCSeconds() === 0
-      && date.getUTCMinutes() === 0
-      && date.getUTCHours() === 0;
-}
-
-function formatYear(year) {
-  return year < 0 ? "-" + pad(-year, 6)
-    : year > 9999 ? "+" + pad(year, 6)
-    : pad(year, 4);
-}
+import {format} from "isoformat";
 
 export default function formatDate(date) {
-  return isNaN(date)
-    ? "Invalid Date"
-    : isUTCMidnight(date)
-      ? formatYear(date.getUTCFullYear()) + "-" + pad(date.getUTCMonth() + 1, 2) + "-" + pad(date.getUTCDate(), 2)
-      : formatYear(date.getFullYear()) + "-" + pad(date.getMonth() + 1, 2) + "-" + pad(date.getDate(), 2)
-        + "T" + pad(date.getHours(), 2) + ":" + pad(date.getMinutes(), 2)
-        + (date.getMilliseconds() ? ":" + pad(date.getSeconds(), 2) + "." + pad(date.getMilliseconds(), 3)
-          : date.getSeconds() ? ":" + pad(date.getSeconds(), 2)
-          : "");
+  return format(date, "Invalid Date");
 }