Add support for months

Upstream issue: vercel#57

src/index.ts

@@ -4,6 +4,7 @@ const m = s * 60;
 const h = m * 60;
 const d = h * 24;
 const w = d * 7;
+const mo = d * 30;
 const y = d * 365.25;
 
 type Unit =
@@ -12,6 +13,9 @@ type Unit =
   | 'Yrs'
   | 'Yr'
   | 'Y'
+  | 'Months'
+  | 'Month'
+  | 'Mo'
   | 'Weeks'
   | 'Week'
   | 'W'
@@ -92,7 +96,7 @@ export function parse(str: string): number {
     );
   }
   const match =
-    /^(?<value>-?(?:\d+)?\.?\d+) *(?<type>milliseconds?|msecs?|ms|seconds?|secs?|s|minutes?|mins?|m|hours?|hrs?|h|days?|d|weeks?|w|years?|yrs?|y)?$/i.exec(
+    /^(?<value>-?(?:\d+)?\.?\d+) *(?<type>milliseconds?|msecs?|ms|seconds?|secs?|s|minutes?|mins?|m|hours?|hrs?|h|days?|d|weeks?|w|months?|mo|years?|yrs?|y)?$/i.exec(
       str,
     );
   // Named capture groups need to be manually typed today.
@@ -110,6 +114,10 @@ export function parse(str: string): number {
     case 'yr':
     case 'y':
       return n * y;
+    case 'months':
+    case 'month':
+    case 'mo':
+      return n * mo;
     case 'weeks':
     case 'week':
     case 'w':

src/parse-strict.test.ts

@@ -115,6 +115,12 @@ describe('parseStrict(long string)', () => {
     expect(parseStrict('1 week')).toBe(604800000);
   });
 
+  it('should convert months to ms', () => {
+    expect(parseStrict('1 month')).toBe(2592000000);
+    expect(parseStrict('3 months')).toBe(2592000000 * 3);
+    expect(parseStrict('2 mo')).toBe(2592000000 * 2);
+  });
+
   it('should convert years to ms', () => {
     expect(parseStrict('1 year')).toBe(31557600000);
   });