Using fs.watchFile if supported, fs.watch otherwise (fixes #1803)

src/command.coffee

@@ -168,22 +168,33 @@ loadRequires = ->
   require req for req in opts.require
   module.filename = realFilename
 
-# Watch a source CoffeeScript file using `fs.watch`, recompiling it every
-# time the file is updated. May be used in combination with other options,
-# such as `--lint` or `--print`.
+# Watch a source CoffeeScript file using `fs.watchFile` (or, if unsupported,
+# `fs.watch`--see #1803), recompiling it every time the file is updated. May
+# be used in combination with other options, such as `--lint` or `--print`.
 watch = (source, base) ->
-  fs.stat source, (err, prevStats)->
+  fs.stat source, (err, prevStats) ->
     throw err if err
-    fs.watch source, (event) ->
-      if event is 'change'
-        fs.stat source, (err, stats) ->
-          throw err if err
-          return if stats.size is prevStats.size and 
-            stats.mtime.getTime() is prevStats.mtime.getTime()
-          prevStats = stats
-          fs.readFile source, (err, code) ->
+    onChange = ->
+      fs.readFile source, (err, code) ->
+        throw err if err
+        compileScript(source, code.toString(), base)
+
+    if fs.watchFile
+      try
+        fs.watchFile source, {persistent: true, interval: 500}, (curr, prev) ->
+          onChange() unless curr.size is prev.size and curr.mtime.getTime() is prev.mtime.getTime()
+      catch e
+        watchFileUnsupported = true
+
+    if watchFileUnsupported or !fs.watchFile
+      fs.watch source, (event) ->
+        if event is 'change'
+          fs.stat source, (err, stats) ->
             throw err if err
-            compileScript(source, code.toString(), base)
+            return if stats.size is prevStats.size and
+              stats.mtime.getTime() is prevStats.mtime.getTime()
+            prevStats = stats
+            onChange()
 
 # Write out a JavaScript source file with the compiled code. By default, files
 # are written out in `cwd` as `.js` files with the same name, but the output