ADD: Eq, Ord, and Show instances for JSDate (#17)

* ADD: Eq, Ord, and Show instances for JSDate

* ADD: fromTime to export list

src/Data/JSDate.js

@@ -63,3 +63,7 @@ exports.parse = function (dateString) {
     return new Date(dateString);
   };
 };
+
+exports.fromTime = function (time) {
+  return new Date(time);
+};

src/Data/JSDate.purs

@@ -43,6 +43,7 @@ module Data.JSDate
   , toString
   , toTimeString
   , toUTCString
+  , fromTime
   ) where
 
 import Prelude
@@ -66,6 +67,15 @@ import Data.Time.Duration (Milliseconds(..))
 -- | The type of JavaScript `Date` objects.
 foreign import data JSDate :: Type
 
+instance eqJSDate :: Eq JSDate where
+  eq a b = getTime a == getTime b
+
+instance ordJSDate :: Ord JSDate where
+  compare a b = getTime a `compare` getTime b
+
+instance showJSDate :: Show JSDate where
+  show a = "(fromTime " <> show (getTime a) <> ")"
+
 -- | The effect type used when indicating the current machine's date/time locale
 -- | is used in computing a value.
 foreign import data LOCALE :: Effect
@@ -263,3 +273,6 @@ toTimeString dt = runFn2 dateMethod "toTimeString" dt
 -- | Returns the date as a string using the UTC timezone.
 toUTCString :: JSDate -> String
 toUTCString dt = runFn2 dateMethod "toUTCString" dt
+
+-- | Returns the date at a number of milliseconds since 1970-01-01 00:00:00 UTC.
+foreign import fromTime :: Number -> JSDate

test/Test/Main.purs

@@ -60,6 +60,18 @@ main = do
   assert $ JSD.toDateTime (JSD.fromDateTime bottom) == Just bottom
   assert $ JSD.toDateTime (JSD.fromDateTime top) == Just top
 
+  log "Check that equal dates test equal"
+  assert $ JSD.fromDateTime dateTime == JSD.fromDateTime dateTime
+  assert $ JSD.fromDateTime ancientDateTime == JSD.fromDateTime ancientDateTime
+
+  log "Check that unequal dates do not test equal"
+  assert $ JSD.fromDateTime dateTime /= JSD.fromDateTime ancientDateTime
+
+  log "Check that dates are chronologically ordered"
+  assert $ JSD.fromDateTime dateTime `compare` JSD.fromDateTime dateTime == EQ
+  assert $ JSD.fromDateTime dateTime `compare` JSD.fromDateTime ancientDateTime == GT
+  assert $ JSD.fromDateTime ancientDateTime `compare` JSD.fromDateTime dateTime == LT
+
   log "All tests done"
 
   where