implement %o to get the day of the month as an ordinal

Readme.md

@@ -73,6 +73,7 @@ e.g. `%q` becomes `q`. Use `%%` to get a literal `%` sign.
 - M: the minute, padded to 2 digits (00-59)
 - m: the month, padded to 2 digits (01-12)
 - n: newline character
+- o: day of the month as an ordinal (without padding), e.g. 1st, 2nd, 3rd, 4th, ...
 - P: "am" or "pm" in lowercase [Ruby extension]
 - p: "AM" or "PM"
 - R: equivalent to `%H:%M`

strftime.js

@@ -122,6 +122,7 @@
         case 'M': return pad(d.getMinutes(), padding);
         case 'm': return pad(d.getMonth() + 1, padding);
         case 'n': return '\n';
+        case 'o': return String(d.getDate()) + ordinal(d.getDate());
         case 'P': return d.getHours() < 12 ? locale.am : locale.pm;
         case 'p': return d.getHours() < 12 ? locale.AM : locale.PM;
         case 'R': return _strftime(locale.formats.R || '%H:%M', d, locale);
@@ -204,6 +205,21 @@
     return hour;
   }
 
+  // Get the ordinal suffix for a number: st, nd, rd, or th
+  function ordinal(n) {
+    var i = n % 10
+      , ii = n % 100
+      ;
+    if ((ii >= 11 && ii <= 13) || i === 0 || i >= 4) {
+      return 'th';
+    }
+    switch (i) {
+      case 1: return 'st';
+      case 2: return 'nd';
+      case 3: return 'rd';
+    }
+  }
+
   // firstWeekday: 'sunday' or 'monday', default is 'sunday'
   //
   // Pilfered & ported from Ruby's strftime implementation.

test/test.js

@@ -84,6 +84,7 @@ assert.format('%0l', null, '06')
 assert.format('%M', null, '51')
 assert.format('%m', '06')
 assert.format('%n', '\n')
+assert.format('%o', '7th')
 assert.format('%P', null, 'pm')
 assert.format('%p', null, 'PM')
 assert.format('%R', null, '18:51')