From 41d900cfd4e99b3025697e96ba4d3637dbcf632a Mon Sep 17 00:00:00 2001
From: Kunal Marwaha <marwahaha@berkeley.edu>
Date: Wed, 29 Mar 2017 02:35:52 -0400
Subject: [PATCH] Calculate daysInMonth without Date()

---
 src/lib/units/month.js | 11 ++++++++++-
 src/lib/units/year.js  |  2 +-
 src/lib/utils/mod.js   |  3 +++
 3 files changed, 14 insertions(+), 2 deletions(-)
 create mode 100644 src/lib/utils/mod.js

diff --git a/src/lib/units/month.js b/src/lib/units/month.js
index 28b4a1b98..6f682f3f8 100644
--- a/src/lib/units/month.js
+++ b/src/lib/units/month.js
@@ -10,12 +10,21 @@ import { MONTH } from './constants';
 import toInt from '../utils/to-int';
 import isArray from '../utils/is-array';
 import isNumber from '../utils/is-number';
+import mod from '../utils/mod';
 import indexOf from '../utils/index-of';
 import { createUTC } from '../create/utc';
 import getParsingFlags from '../create/parsing-flags';
+import { isLeapYear } from '../units/year';
 
 export function daysInMonth(year, month) {
-    return new Date(Date.UTC(year, month + 1, 0)).getUTCDate();
+    if (isNaN(year) || isNaN(month)) {
+        return NaN;
+    }
+    var modMonth = mod(month, 12);
+    if (modMonth === month) {
+        return month === 1 ? (isLeapYear(year) ? 29 : 28) : (31 - month % 7 % 2);
+    }
+    return daysInMonth(year + (month - modMonth) / 12, modMonth);
 }
 
 // FORMATTING
diff --git a/src/lib/units/year.js b/src/lib/units/year.js
index a10e5b4be..8f3f94cda 100644
--- a/src/lib/units/year.js
+++ b/src/lib/units/year.js
@@ -56,7 +56,7 @@ export function daysInYear(year) {
     return isLeapYear(year) ? 366 : 365;
 }
 
-function isLeapYear(year) {
+export function isLeapYear(year) {
     return (year % 4 === 0 && year % 100 !== 0) || year % 400 === 0;
 }
 
diff --git a/src/lib/utils/mod.js b/src/lib/utils/mod.js
new file mode 100644
index 000000000..8046cdac9
--- /dev/null
+++ b/src/lib/utils/mod.js
@@ -0,0 +1,3 @@
+export default function mod(n, x) {
+    return ((n % x) + x) % x;
+}
-- 
2.47.2