Add snippet for formatSeconds

snippets/formatSeconds.md

@@ -0,0 +1,26 @@
+---
+title: formatSeconds
+tags: date,math,string
+---
+
+Returns the ISO format of the given number of seconds.
+
+- Divide `s` with the appropriate values to obtain the appropriate values for "HH:mm:ss".
+- Use `Array.prototype.map()` to create the string for each value, and pads it to `2` digits.
+- Use `String.prototype.join(', ')` to combine the values into a string.
+
+```js
+const formatSeconds = s => {
+  if (s < 0) s = 0;
+  
+  return [s / 3600, s / 60 % 60, s % 60]
+  	.map(v => `${Math.floor(v).toString().padStart(2, '0')}`)
+  	.join(':');
+};
+```
+
+```js
+formatSeconds(-200); // "00:00:00"
+formatSeconds(200); // "00:03:20"
+formatSeconds(99999); // "27:46:39"
+```